carbonation of ca based waste materials from fbc...

Carbonation of Ca Based Waste Materials from FBC Boilers 1

By E.J. Anthony and L. JiaCETC, Natural Resources Canada

1 Haanel Drive, Ottawa, Ontario, Canada K1A 1M1E-mail: [email protected]

ABSTRACTThe use of high sulphur fuels in Fluidized Bed Combustion (FBC) results in high CaO contents for the resulting ashes. As a result the ashes react exothermically with water, produce high pH leachate, and are also subject to significant and uncontrolled expansion in the landfill, both of which factors add significantly to the disposal cost of the resulting FBC ashes. The current disposal practices involve a two-step hydration process, which is not particularly effective, and does not resolve either the problem of high pH leachate or expansion. Carbonation (i.e. reaction with CO2 from the flue gases) offers a method of resolving all of these difficulties and depending on the sulphur content of the coal, also offers a method of reducing boiler CO2 emissions by several percent. However, direct carbonation by using high pressures or temperatures is not sufficiently fast to make a viable conversion process. Work at CETC however, has shown that sonic energy both in its low frequency and high frequency version is capable of accelerating the carbonation process, and allowing the full range of ashes from a FBC to be quantitatively converted to CaCO3. This approach, which has been patented by CETC, has been demonstrated at both bench-scale using ultrasound and industrial-scale using low frequency sound (100-500 Hz) which have been shown to be equivalent in their performance. This paper discusses the experimental work done by CETC and examines the feasibility of this approach for the treatment of high calcic ashes from industrial-scale FBC boilers.

2BIOREACTOR LANDFILLS: TRANSPORT PROCESSES AND CHEMICAL ENGINEERING

PERSPECTIVES

Don Augenstein, I E M, Palo Alto, CA 943061

Bioreactor landfills are receiving increased attention as their possible benefits are recognized. Among benefits potentially available are waste volume reduction and landfill life extension, greater energy recovery, and lowered long-term care. A number of other benefits have been covered in SWANA's recent White Paper (Pacey et. al., 1999).

Landfill bioreactors are actually fermentation processes, of a unique sort. They have no close parallel among "classical" fermentation operations for antibiotic, ethyl alcohol and other product manufacture, or even in wastewater treatment or manure digestion to methane. Small-scale lysimeter tests may not address or replicate important phenomena to be expected at the much larger scales of operating landfills. Some important issues arising in the realm of biochemical engineering (chemical/biological reactions and transport processes) with fullscale bioreactors include:

1. Thermal and heat transfer effects.

Anaerobic bioreactors generate sufficient heat from biological and other reactions to elevate temperature by several tens of degrees. The generated heat can be estimated from enthalpies of reactions such as methane generation. It can be shown that the generated heat tends to be retained; with conduction out of deep landfills extremely slow (time constant, order of decades) The generated heat in turn affects reaction speed; Over a range of 40-135F, the speed of anaerobic methane generation seems well described by classical temperature dependence (Arrhenius relation). Practical consequences are that enough heat can be generated anaerobically to either speed reactions, or, if there is too much heat, (> 135-140F) to cause anaerobic processes to "cook to a stop". There has been evidence for both of these in field demonstrations (several thousand ton scale) to date.

For aerobic bioreactors, generated heat be 10-20 times that of anaerobic for each pound of waste destroyed (i. e. completely oxidized biologically to CO2/H2O). Analyses suggest generated heat could easily require centuries to dissipate from landfills if heat loss by conduction alone. In practice it appears heat must be lost via latent heat of evaporation of water into the air stream passing through the aerobic landfill. To biologically convert a pound of waste, about 5-7 pounds of water much reach the waste and be evaporated to dissipate the heat. Furthermore, sufficient air must permeate waste to evaporate the necessary water. Calculations show that air volumes needed for aerobic waste decomposition are about two orders of magnitude greater than the potential landfill gas potential from decomposition of the same waste. The energy to pump the air through the waste can be high. The need to dissipate heat places constraints on aerobic bioreactors that may in turn limit how fast waste can be consumed. The high air throughput that appears necessary has implications both in terms of material balances and also with respect any gas-phase methane or other organic compound emissions of concern.

2. Mass transfer effects and limitations.

Early analyses (1970's) of methane generation from solid waste. examined possible rate-limiting steps including diffusional transfer of intermediates One surprising result of such calculations was that, given adequate moisture, diffusional transport limitations do not appear serious in anaerobic processes, i. e. diffusional mass transfer will generally not limit rates. One implication is that little or no further mixing or recirculation would be required providing all components can be sufficiently mixed initially. However, it is possible to envision many cases ("gedanken" situations) where substantial effort, such as recirculation, must continue for some time to obtain the necessary initial contacting. Such situations are likely, and will be discussed

1 Abstract to be considered for International Landfill Conference, Lulea, Sweden, December, 2000

For aerobic bioreactors, transport of oxygen necessary for waste destruction may limit rates and/or conversion. This is in part due to sparing solubility of oxygen so that oxygen transport rates into water or biofilms surrounding waste elements may be slow. It is also in part due to the fact that oxygen may bypass waste within the landfill, i. e., there could be "channeling". Example calculations show that oxygen diffusion could easily be a limiting factor as waste consumption progresses. Another possible adverse effect, if insufficient water reaches a given zone within waste, is development of a zone of dry waste where reactions cease within the aerobic landfill.

Another transport-related phenomenon of interest is convective and conductive heat transfer to and from, and consequent temperature elevation of, bioreactors' base layers. For certain combinations of parameters, transfer of heat by warm liquid percolating to base layers over longer terms may be such as to substantially elevate base layer temperature. Limited experimental data bear this out, and base layer performance under such conditions must be assured.

Certain interrelations among parameters can be predicted. These include relationships among water consumption, air throughput, and waste destruction for aerobic bioreactors, and between degree of waste decomposition and temperature elevation for anaerobic bioreactors. Solutions are available, in principle, for some of the apparent hurdles such as heat generation in bioreactor operation. The interrelations that seem clear-cut, and also some possible solutions to problems, will be described. For many other performance parameters of interest, (for example degrees of gas channeling) the situation is complex. There is not enough information for modeling; the answers are only likely to be obtained through careful performance monitoring at large scale. Such measurement and testing has been very limited to date. This presentation will cover some large-scale testing needs as well.

3Abstract

SUBMITTED TO THE INTERNATIONAL LANDFILL RESEARCH SYMPOSIUM

LULEA UNIVERSITY OF TECHNOLOGY LULEA, SWEDEN,

DECEMBER 11-13, 2000

Methane Oxidation in Simulated Landfill Cover Soils

Z. Bajic, MEng and C. Zeiss, Ph.D., P.Eng, Assoc. Prof.

Department of Civil & Environmental Engineering,University of Alberta, Edmonton, AB

Canada T6G 2M8Tel. (780) 492-0708Fax (780) 492-8289

Email: [email protected]

With about 40 to 70 Mt of methane emitted each year worldwide, landfills are the largest anthropogenic source of this greenhouse gas in North America. Landfill gas collection reduces methane emissions by 50 to 60%. The remaining 40 to 50% of landfill gas is emitted to the atmosphere. While the number and the efficiency of landfill gas extraction systems is increasing, other significant reductions of methane emissions from landfills are necessary. Methane oxidation in the top cover soil layer has been shown to provide a methane emission reduction potential of 10 to 70% of the methane produced.

This study was conducted to evaluate the effects of different materials, used to simulate landfill cover soils, tested under different conditions. By creating optimal ambient conditions for methanotrophic bacteria in cover layers, it is possible to increase the microbial activity and to attain very high oxidation rates. Temperature, moisture content, and oxygen penetration are among the most important factors for methane oxidation. The main goal of this research is to find a material or a mixture of materials that optimize all factors and provide the highest rate of methane oxidation. The final results will be applied to engineer the design and to improve the operational conditions of landfill surface covers applicable on different types of landfills with or without collection systems.

A test series of six column reactors was conducted. Each column was constructed from 20 cm diameter PVC pipe containing a 50 cm thick layer of soil. The columns were filled with 1) soil (mixed clay, silt, and sand), 2) soil & compost, 3) soil & sand, 4) soil & pulp sludge, and 5) clay & soil. The sixth column was filled with soil and run at low temperature. The columns were fed from below by synthetic landfill gas, composed of a 45:45% mixture of methane and carbon dioxide, and 10% neon (used as a tracer gas). A gas flow flux was 2.3410-7g CH4 cm-2d-1, which was lower midrange of reported landfill methane fluxes. Atmospheric conditions were maintained at the top of the soil where air inflow was 300 mL min -1. Fresh soil was collected from the Clover Bar Landfill, an active municipal landfill in Edmonton, Canada. All materials were air-dried prior to filling of the columns.

Our results showed the constant presence of methane oxidation even under low temperature (4C) and low moisture content (5-10% by volume). A mixture of 50:50 vol.% of soil and pulp sludge showed methane reduction of between 65% and 85% of the applied flux with the reduction rate of about 150 g of CH4 m-2d-1. This rate is very close to the methane oxidation potential rate measured for the same soil by incubation tests before. Under lower moisture content the intensity of the reaction is the same throughout the entire depth, while an increase in moisture content limits oxygen penetration so that the most intensive reaction occurs at 15 to 25 cm of depth.

In the next planned phase of research, field scale tests with the best soil profile from the column tests, will be performed, based on the findings of the lab tests. These tests will be performed under actual atmospheric conditions over a 12-month period. During winter the oxidation layers will be insulated. The significance of these tests is to develop an engineered cover layer that will passively reduce greenhouse gas

mailto:[email protected]

emissions. This approach is applicable as a stand-alone method at smaller, remote and older landfills (where gas generation is low, or gas use infeasible), or in conjunction with landfill gas extraction at large landfills to reduce the part of methane that can not be collected.

4The Incubation Test -

Development of a Test Method Describing the Biological Reactivity of Mechanically-Biologically Pretreated Waste

Erwin BINNER, Alexander ZACH

Universität für Bodenkultur Wien (University of Agricultural Sciences, Vienna)IWGA, Department Waste Management

Nußdorfer Lände 29-31, A-1190 Vienna, AustriaTel.: ++43-1/ 318 99 00

e-mail: Erwin Binner <[email protected]>

Abstract:

The Austrian Landfill Ordinance allows the disposal of mechanically-biologically pretreated wastes in a so-called „Massenabfalldeponie“, if their calorific value is less than 6,000 kJ/kg DM. The calorific value describes the potential energy gained in an incineration process but is not intended to describe the reactivity. In 1994 we started to develop an anaerobic test method (incubation test) describing the gas-generating potential of MBP-wastes. This test method allows to reproduce a majority of “natural conditions” in the laboratory. Large sample sizes (> 1 kg DM), robust test conditions and easy handling ensures good reproduction of results even for the purpose of self control in MBP-facilities.

Two research programs (1996 to 1999) sponsored by the Austrian Ministry of Environment showed, that the results of the incubation test (gas production GS21, test-duration 21 days) correlate significantly (r = 0.956, 27 samples of well pretreated wastes) to the whole gas-generating potential (gas production in 240 days) as well as to the respiration activity test (AT4, test-duration 4 days, r = 0.912, 27 samples).

For the incubation test a moist fresh sample sieved to Æ 20 mm with approximately 1.5 kg dry matter is saturated to water-holding capacity and then incubated in a glass reactor under anaerobic conditions at 40°C (water bath). Gas generation is measured by a so-called "eudiometertube" and calculated to normal-conditions (0°C, 1013 mbar). Because of the big amount of sample only 2 repetitions are necessary. Even though gas generation is often not yet finished after 240 days, it is still possible to make an adequately accurate assessment after 21 days.

In contrast to the fermentation test (50 g moist fresh sample ground to Æ 10 mm, diluted up to 300 ml) the incubation test does not need inoculation. Normally the anaerobic degradation process starts very soon, if waste is sufficiently pretreated. However, untreated or very shortly treated wastes often show long lag phases because of acidification, which may pretend low reactivity. Lag-phases and low reactivity can be recognized by different curves of cumulative gas-generation, by measuring pH-value and analyzing the methane content in the generated gas. Concave curves (Fig.1), pH-values lower than 6,5 and methane contents < 55 % are typical for lag-phases. Convex curves, pH-values > 7 and methane contents > 60 % characterize low reactive materials. If lag-phases occur, test duration must be extended.

The advantages of the incubation test are: no inoculum needed (no problems with preparation and storage of inoculum) good reproduction because of the large amount of sample (1.5 kg DM) for each sample only duplicate analysis is sufficient (2 test cells - in contrary to the fermentation

test where 7 test cells are necessary) well pretreated materials still produce measurable amounts of gas – in contrary, in the fermentation

test gas amounts are hardly detectable due to the low amount of sample

Cumulative Gas Generation in the Incubation Test

Test Duration [days]

Gas

Gene

ratio

n [N

l/kg

DM

]

0

5

10

15

20

0 30 60 90

5 weeks pretreatment

16 weeks pretreatment

21 days

well pretreated material(convex curve)

shortly pretreated material(lag-phase, concave curve)

Fig. 1: Cumulated gas generation in the incubation test. The different types of the curves allow to recognize either lag-phases (concave curve) or low reactivity (convex curve).

The Development of Low Cost Landfilling Techniques for Emerging Countries

5M Caine(a) and M Pugh

(a) Corresponding AuthorMalcolm CainePrincipal ConsultantWaste Management GroupAEA Technology EnvironmentCulham Science and Engineering CentreAbingdonOxonUKOX14 3DB

Tel: 44 (0)1235 463056Fax: 44 (0) 1235 463010e-mail: [email protected]

AbstractThe UK Department for International Development has commissioned a project with the aim of demonstrating and evaluating through field trials improved low-cost landfilling techniques suitable for application in developing countries. A particularly important objective of the project is to demonstrate how, with better disposal practices, the protection of water resources can be greatly enhanced. The field-scale landfills will be located in Thailand and South Africa to enable the assessment of tropical and temperate climates on the landfilling techniques used. Beyond the protection of water resources the field studies will demonstrate a number of additional benefits including:

Illustration of low-cost techniques to confine, place, and cover wastes in a more environmentally acceptable manner;

reduction of wind-blown litter and waste burning (by operations which rapidly cover waste deposits, and by better management to control on-site activities of scavengers);

improvement of environmental quality in the vicinity of the deposits (eliminating smoke emissions and litter and reducing the potential for disease due to vector activity on wastes);

demonstration of routine monitoring to confirm the environmental acceptability of landfilled wastes.

The programme of work began in 1999, and is scheduled for completion in 2003. The initial outputs were a literature review characterising the state of the art in this area and preparing detailed designs for the two pilot scale sites. This work has been completed for both countries and currently the sites are being filled with wastes using simple, readily available plant such as a JCB type backhoe excavator.

This paper will review the project to-date, providing a summary of the state of the art of low cost landfill techniques and an overview of the design of each pilot landfill. Data gained from the operational period including filling rates, bulk densities, rates of leachate evolution, leachate quality will be presented and compared to conventional landfill. Other operational information gathered during the filing phase will also be summarised.

The presentation will incorporate video footage from each location to illustrate the techniques evaluated.

Interim conclusions of the work will be presented as well as lessons learned.

The presentation will conclude with our plans for dissemination of the overall conclusions of the project to decision makers and operational managers in emerging countries via the world Bank collaborative working group, regional workshops and through the internet.

END

6Abstract for Luleå 2000, Intercontinental Landfill Research Symposium, 11-13 December 2000, Luleå University of Technology, Luleå, Sweden

Suggested session: Landfill gas emissions: New measurements and supporting studiesDestination: Oral presentation

FACTORS GOVERNING LATERAL GAS MIGRATION AND SUBSEQUENT EMISSION IN SOIL ADJACENT TO AN OLD LANDFILL

Mette Christophersen2 & Peter KjeldsenDepartment of Environmental Science and Engineering

Technical University of Denmark, Building 115DK-2800 Lyngby, Denmark

Introduction

The migration and emission of landfill gas (LFG) may potentially lead to negative effects in the surroundings, for example; fire and explosion hazards, health risks, damage to vegetation, odour nuisances, groundwater contamination, and global climate effects (Kjeldsen, 1996). The main environmental hazards related to LFG are believed to be the explosion hazards and the global climate effects. Over a 100-year span, methane has a global warming potential of 21 (kg CH4/kg CO2) because of its stronger molar absorption coefficient for infra red radiation and longer residence time in the atmosphere (Lelieveld, 1998).

Barometric pressure is believed to be a major factor controlling methane emissions from landfills. A decline in barometric pressure will draw out landfill gas, while increases in barometric pressure will results in decline in landfill gas emissions.

Many older landfills, which are placed in abandoned gravel pits are unlined, and compacted waste and impermeable top covers encourage lateral gas migration. However no one has investigated emissions of LFG from soils adjacent to landfills. The objective of this study was to investigate lateral gas migration and subsequent emissions in soil adjacent to an old municipal landfill, in order to determine the most important controlling factors.

MethodsThe field investigations were carried out at Skellingsted Landfill, Denmark. The landfill received domestic and industrial waste from 1971 to 1990. The landfill is placed in an old gravel pit and there are no liners. Sampling equipment was installed along two transects with the first station in the top cover of the landfill and the subsequent stations on a line perpendicular to the landfill border. Each transect consisted of 9 measuring stations, and

2 Corresponding author, fax. (+45) 45 93 28 50, e-mail: [email protected]

each station consisted of a stationary flux chamber, soil gas probes to measure gas concentrations and pressure above barometric pressure at 6 depths and probes to measure the volumetric soil moisture content at 5 depths down to 1 m below surface (b.s.). Measuring campaigns were conducted approximately every second week from May 1997 to May 1998 and during a drop in barometric pressure intensive measurements were conducted for two days.

Results & DiscussionIn general the concentrations of landfill gas in the soil varied showing that the lateral gas migration is a

very dynamic system. There was a statistical significantly seasonal variation in the methane concentrations

1 m b.s. Close to the landfill the methane concentrations were low in the summer and significantly higher

in the winter. For the carbon dioxide concentrations the opposite was observed. This was caused by

oxidation of methane to carbon dioxide. Further away from the landfill the concentrations of both methane

and carbon dioxide were statistically significant higher in the winter compared with the summer caused by

the higher soil moisture content in the topsoil in the winter. The higher water content reduced the vertical

gas emission. There were large variations in the measured emissions during the one-year

measuring period, and there was a significantly seasonal variation in the emissions with very low fluxes of methane in the summer and higher fluxes in the winter. For carbon dioxide the seasonal variation was the opposite with high fluxes in the summer and lower fluxes in the winter. These seasonal variations were caused by the temperature dependent methane oxidation. Statistical analysis showed that soil moisture content was the factor describing the largest part of the variation in the fluxes.

Pressure above the barometric pressure was measured in the soil in areas, which was affected by

landfill gas during the measuring period. This indicated that advective flux was important for the gas

migration. The measured gas concentrations and fluxes were used as input to a numeric gas transport

model. The model was used to evaluate the sensitivity of the concentrations and the fluxes to changes in:

methane oxidation, diffusion, gas permeability, barometric pressure and soil moisture content. The results

of the sensitivity analysis indicated that landfill gas migration was most sensitive to air permeability and

soil moisture content, and that diffusion had no influence at all.

The intensive measurements during a drop in the barometric pressure showed a clear connection

between the gas concentrations in the soil, the emissions and the decreasing barometric pressure. The

concentrations and the fluxes increased as the barometric pressure decreased. Large changes in especially

the methane concentrations were observed in the soil within very short time. The changes in both methane

and carbon dioxide fluxes were also large.

ReferencesKjeldsen, P. (1996) Landfill gas migration in soil. In Landfilling of waste: Biogas, (T.H. Christensen, R.

Cossu, & R. Stegmann eds.). London, GB: E & FN Spon.

Lelieveld, J. Crutzen, P. J. & Dentener, F. J. (1998) Changing concentration, lifetime and climate forcing of

atmospheric methane. Tellus 50B, 128-150.



FIELD INVESTIGATIONS OF METHANE OXIDATION IN SOIL ADJACENT TO AN OLD LANDFILL

Mette Christophersen3 & Peter KjeldsenDepartment of Environmental Science and Engineering


Introduction

Landfill gas (LFG) contains high concentrations of methane, and methane from landfills is estimated to 40 Tg out of the total amount of 600 Tg methane emitted to the atmosphere. LFG thereby contributes to the greenhouse effect. Methane is an important greenhouse gas and a more powerful greenhouse gas than carbon dioxide. Over a 100 year span methane has a global warming potential of 21 (kg CH4/kg CO2) (Lelieveld, 1998).

LFG is transported through soil layers in landfill top covers or in adjacent areas before being emitted to the atmosphere. While transported in the soil layers the landfill gas is mixed with atmospheric air, and the methane may be oxidised by the methanotrophic bacteria in the soil. Oxidation of methane in top covers of landfills has been observed at several occasions, and soil exposed to elevated methane concentrations can develop a high capacity for methane oxidation (e.g. Whalen et al., 1990).

There are two main ways to reduce methane emission from landfills. One option is gas recovery with associated gas use, which are very effective at large landfills with high methane generation. At smaller and older landfills with low methane generation it is more effective to encourage methane oxidation in the soil cover of the landfills. In northern Europe there are many small and old landfills with low gas generation, and here methane oxidation is a possible way to manage methane emission. The objective of this study was to investigate methane oxidation in soil adjacent to an old municipal landfill, in order to evaluate the importance of methane oxidation on landfill gas emissions.

MethodsThe field investigations were carried out at Skellingsted Landfill, Denmark. The landfill is placed in an old gravel pit and there are no liners. Sampling equipment was installed along two transects with the first station in the top cover of the landfill and the subsequent stations on a line perpendicular to the landfill border. Each transect consisted of 9 measuring stations, and each station consisted of a stationary flux chamber, soil gas


probes to measure gas concentrations and pressure above barometric pressure at 6 depths and probes to measure the volumetric soil moisture content at 5 depths down to 1 m below surface (b.s.). Air and soil temperatures were measured. Measuring campaigns were conducted approximately every second week from May 1997 to May 1998. To quantify the methane oxidation isotope analysis were conducted at one measuring campaign.

Results & DiscussionAt the Skellingsted landfill many indications of methane oxidation were observed during the one-year measuring period: The CH4/CO2 ratio fell with distance from the landfill and up through the soil profile. Nitrogen concentrations above the atmospheric content was observed as a result of

the volume reduction caused by methane oxidation. Methane oxidation is an exothermic process and the soil was warmer in the areas,

where methane oxidation was occurring. High concentrations of carbon dioxide associated with methane concentrations below

the detection limit in the soil (up till 22% carbon dioxide). Methane fluxes were never measured in the summer however high carbon dioxide

fluxes were found.Box-calculations were conducted to estimate the methane oxidation in the top 1 m of the soil profile. The measured fluxes and concentrations of methane and carbon dioxide were used in the calculations, and it was assumed that no carbon dioxide was dissolved in the pore water and that no gas was produced in the soil. The calculations showed that all the methane was oxidised in the summer. On an annual basis 89% of the lateral migrating methane was oxidised. However isotope analysis of the methane at one measuring campaign showed lower fractions of methane oxidised, compared with the box-calculations in the situations, where methane was detected in the flux chamber. The isotope analysis showed that the largest part of the oxidation was occurring in the top 20 cm of the soil profile.

References

Lelieveld, J. Crutzen, P. J. & Dentener, F. J. (1998) Changing concentration, lifetime and climate forcing of

atmospheric methane. Tellus 50B, 128-150.

Whalen, S.C., Reeburgh, W.S. &. Sandbeck. K.A. (1990) Rapid Methane Oxidation in a Landfill Cover

Soil. Applied and Environmental Microbiology 56, 3405-3411.

8A Multi-Year Study of Gas Emissions to the Atmosphere from a Single Landfill in

the Northeastern United States

Abstract

P.M. Czepiel1, J.H. Shorter2, B. Mosher1, E. Allwine3, B.K. Lamb3, C.E. Kolb2, R.C. Harriss4

1: Complex Systems Research Center, University of New Hampshire, Durham, NH, USA2: Center for Chemical and Environmental Physics, Aerodyne Research Inc., Billerica, MA, USA

3: Laboratory for Atmospheric Research, Washington State University, Pullman, WA, USA4: National Center for Atmospheric Research, Boulder, CO, USA

Landfills are the largest source of methane emissions to the atmosphere in the United States. However, few measurements of whole landfill methane emissions have been reported. Here, we present the results of a multi-year study of whole landfill emissions from a single site using atmospheric tracer methods. The study was conducted at the Nashua, New Hampshire Municipal landfill in the northeastern United States.

The site was initially investigated in October 1994, before the installation of a gas collection system. Methane emissions to the atmosphere at that time ranged from 12,900 to 23,600 l CH4 min-1(n=5). Emissions were also measured in August 1996, February 1997, and April 1997 subsequent to the installation of a gas collection and electrical generating system. Methane emissions to the atmosphere, after the initiation of gas collection, ranged from 8,400 to 28,200 l CH4 min-1(n=12). Gas collection during the measurement period remained fairly constant at approximately 11,500 l CH4 min-1. Both pre- and post-collection system emissions were negatively correlated with surface atmospheric pressure. Linear regressions of these data were highly significant with coefficients of determination, or R2, of 0.84 and 0.95 for the pre- and post-collection system emissions data, respectively. Emissions increased approximately 2-fold before gas collection when pressure decreased from 1026 to 1011 mbar. The pressure effect was even more striking after initiation of gas collection. Emissions increased more than 3-fold over a decreasing pressure range of 1023 to 1007 mbar.

From these data we conclude that, at this site: 1) landfill gas extraction significantly increased the rate of gas production, and 2) high frequency changes (hours to days) in surface atmospheric pressure play a predominant role in determining the magnitude of landfill gas emissions to the atmosphere.

Landfill biogas emissions measurements : qualification and quantification of the pathways of

emitted methane.

9Corresponding author : Muriel DIOT

Centre de Recherches pour l’Environnement, l’Energie et le DéchetZone portuaire de Limay291 avenue D.D.Ducas78 520 LimayFax : 01.30.98.54.99E-mail : [email protected]

Diot M.1, Moreau le Golvan Y.1 , Bogner J.2, Burkhalter R.3, Chanton J.4, Spokas K.5, Tregourès A.6, Saint-Bonnet P.6, Thoby D.6, Schaegis L7.

1 : Centre de Recherches pour l’Environnement, l’Energie et le Déchet, Limay, France.2 : Landfills+, Inc, Wheaton, Illinois, USA.3 : Laboratoire National d’Essais, France.4 : Department of Oceanography, Florida State University, Tallahassee, Florida, USA.5 : Argonne National Laboratory, Chicago, Illinois, USA.6 : Commissariat à l’Energie Atomique, Grenoble, France.7 : ONYX EST (Montreuil sur Barse).

Methane, which is a more potent greenhouse agent than CO2, has increased in atmospheric concentration by a factor of 2 in the past century. For France, national estimates prepared for the United Nations Framework Convention on Climate Change indicate that about 25% of the annual methane emissions are from waste disposal, constituting the second largest source after agriculture.One tonne of municipal solid waste stored in a landfill produces from 120 to 150 m3 biogas within several years. Without any recovery system, the biogas can migrate toward the atmosphere and participate to the greenhouse effect. But, due to its methane content, it can be recovered and represents an attractive alternative source of energy from waste.

The research program METAN aims at identifying and quantifying the various biogas flows on a landfill, in order to establish a methane mass balance. Field measurements have been performed on the CGEA-ONYX Montreuil/Barse MSW Landfill (VIVENDI group). Several techniques have been used to quantify the biogas collected, the biogas emitted towards the atmosphere and the biogas oxidised through the cover.A broad range of configurations has been investigated : (i) an active cell, (ii) a temporary covered cell, (iii) two experimental cells made of different top cover configurations and (iv) areas with and without gas recovery.

The adopted strategy to quantify the emitted biogas was to use complementary approaches.Infra Red thermography locates the thermal anomalies of the site potentially due to emitted zones.Surface fluxes were measured by a global method based on tracers, and a local one based on the static chamber method : the tracer method relies on concurrent concentration measurements for the methane and an inert tracer gas (here SF6) released at a known rate above the landfill; the static chamber method is used to measure methane fluxes from small areas of the landfill surface (here 0.25 m²). These involve the placement of a chamber on top of the ground surface for short measuring periods. The flux is calculated from the change in chamber methane concentration with time and the chamber volume/area ratio.In addition, a stable isotopic study was conducted to determine the major pathways of methane emission from the landfill and the portion of methane oxidised during transit from the landfill surface. Samples of methane were collected from the plume of air downwind of the landfill. Methane within these samples integrate the total emission for methane from the landfill. Specific samples were also collected from all major sites of potential emission including from ventilation pipes, from pipes harvesting methane from the

subsurface and from bubbles of landfill gas effusing from cracks and borders of landfill cells. To calculate methane oxidation, the 13C signature of emitted methane will be contrasted with methane collected from anoxic zone samples. The difference in the isotopic signature of these two pools of methane is directly attributable to the fraction of methane oxidised. The technique works because methanotrophic bacteria are known to consume 12CH4 preferentially over 13CH4. This preference and the bacterial fractionation factor associated with methanotrophy were also determined by incubating soils samples at in situ temperatures.

The first results of the tracer method show that the emissions of methane ranges from 8 to 400 Nml.m-

2.min-1 depending on the area of the cells. The highest flux occurs in the operating zone while the lowest flux occurs in the cell with clay cover and biogas recovery. The methane flow emitted by the cell with clay cover represents only 2% of the methane flow emitted by the operating cell. When the gas recovery system is turned off, the flux of methane measured on the same cell is increasing by a factor of two.The chamber measurements are not in accordance with tracers experiments, but they showed that the surface biogas fluxes are localised near the ?discontinuity as leachate wells. Oxidation rates will be soon available.

The results of these field measurements on the two experimental cells in Montreuil will be integrated in a methane mass balance model which is under development.

Kinetics of CH4 oxidation in mixed culture 10

Yutaka DOTEDepartment of Civil and Environmental Engineering, Miyazaki University1-1 Gakuenn Kibanadai Nishi, Miyazaki 889-2155, JapanTel: +81-985-58-7340, Fax: +81-985+58+7344, e-mail: [email protected]

ABSTRACT

Methane is known as a ‘greenhouse‘ gas and produced in large quantities from a wide

range of sources such as swamps, marshes, and paddy fields. Municipal solid waste

landfill sites are one of the methane production sources. The main paths of methane

emission from a landfill site are cover soils and gas venting pipes. A lot of research on

the potential of cover soils to oxidize methane has been reported. Another place where

methane can be oxidized is gas-venting pipes. To design a device for methane oxidation

in gas venting pipes by aerobic microorganisms, it is necessary to clarify the CH4

oxidation rate at various CH4 and O2 concentrations.

Although many researches on kinetics of CH4 oxidation were reported, the effect of O2

concentration was scarcely discussed. The purpose of this paper is to determine the

kinetics of CH4 oxidation and included parameters at various CH4 and O2 concentrations.

Cultures used for CH4 oxidation experiments were prepared by enrichment of extract

from a digested sewage sludge, park soil, or leachate from two landfill sites under 20 %

of CH4, but not isolated. Therefore, the cultures were the mixture of CH4 oxidizing and

other aerobic microorganisms. The CH4 oxidation experiments were conducted with a

batch reactor in which the change in gas volume can be measured. The mixture of air and

CH4 was introduced; initial CH4 concentrations were ranged from 5 % to 20 %.

CH4 oxidation was expressed as a Monod equation for CH4 and first order reaction for O2.

A determined half saturated constant (Km) was 7.5×10-5-7.1×10-4 (mol/L), and a

maximum oxidation rate (Vmax) was 3.8×10-14-3.9×10-11 (mol/hr/cell). The mole ratio of

consumed O2 to CH4 was 1.6-1.8.

Matti Ettala 11Risto Rytin kuja 2 B 19, 00570 Helsinki, [email protected]: +358-9-6848 068

Petri VäisänenSepontie 1Ä, 02130 Espoo, [email protected]: +358-9-4691 329

NEW TECHNOLOGY TO ENHANCE METHANE OXIDATION AT LANDFILLS

Methane oxidation occurs in the upper part of the landfill. However, when soil with low hydraulic conductivity is used in the top cover, landfill gas is discharged from gas wells and methane oxidation is decreased. When landfill gas quantity or concentration is low active gas extraction systems are not applied. Passive landfill gas venting systems have been combined with biological filtering units but because of low oxidation capacity the use of biofilters have not been economical and efficient enough.

In this study new technology has been developed in order to utilize methane oxidation capacity of the whole landfill top cover. Landfill gas is discharged through the sealing layer via landfill gas wells to the drainage layer. That is how landfill gas is delivered all over the landfill and gas flows through the oxidating top cover layer. No pumps are needed. However, homogenity of the top cover has to be taken care of in order to avoid shortcuts of the gas.

Experimental field 50 m * 50 m in size was built at the landfill in Lohja in Finland in January 2000. The first measuring period in May 2000 gave promising results. 121 measurements of methane were made with FID-analyser. In most points methane concentration in the gas flow through the top cover was less than 1 ppm. In five points methane concentration was 6-21 ppm and in one point 245 ppm. Soil temperature was 8-30 oC. Further developments have been planned to be carried out in the next three fields to be built in summer 2000. Landfill gas will be delivered to the drainage layer via drainage pipes in order to achieve controlled gas flow. The new landfill gas delivery system via drainage layer to enhance methane gas oxidation is effective as well as labor and cost saving alternative for biofilters and flares.



Microbial oxidation of landfill methane in a biofilter 12Catherine M. Fischer1 and Marco Bichsel2

1 Laboratory of microbiology, University of Neuchâtel, Emile Argand 11, case postale 2, CH-2007 Neuchâtel 7, Switzerland, tel: 032 718 2251, fax: 032 718 2230, e-mail: [email protected] (corresponding author)2 TDU GmbH, Konzerthallenstrasse 8, Postfach 129, CH-4513 Langendorf, Switzerland

Methane production in a landfill lasts for decades after its closure and requires continuous monitoring and abatement measures over extended periods, e.g. active extraction and flaring of the gas. The methane oxidation potential of the cover soil of landfills is now being increasingly investigated, in view of reducing the amount of methane that escapes to the atmosphere. The rates of methane oxidation measured in landfill-soil microcosms permeated with methane are the highest that have been observed to date in natural soils. Biofilters have also been suggested as a cheaper alternative to flaring for landfill gas, to degrade the malodorous or greenhouse compounds it contains, in particular for hydrogen sulphide and chlorinated hydrocarbons, generally present at low concentrations (0-1%), but also for methane, present at much higher concentrations (up to 55%). This could be particularly interesting once the methane production in a landfill has abated due to exhaustion of the substrate, so that its concentration in the gas extracted has fallen below combustible levels (<5%). The rates of methane oxidation obtained experimentally to-date may be sufficient to intercept most of the methane diffusing extensively up from the waste through the cover soil. However, they are still too low to allow for the intensive oxidation in the comparatively much smaller volume of a biofilter of methane from actively extracted landfill gas, which even in a small landfill is of the order of several m-3 h-1.We will present here the first results of a pilot biofilter for methane oxidation, where various techniques were tested in view of increasing the efficiency of the degradation. We will among others focus on the possibilities offered by thermophilic methanotrophs, a group whose potentialities have been little studied to date.

The Possibility to Minimise the Leachate by Using Compost Substrates and Fast Growing Fuel Plants as a Recultivation Cover on Landfills 13

Tanja Gomiscek and Peter Lechner Universität für Bodenkultur (University of Agricultural Sciences, Vienna), Institute of

Water Provision, Water Ecology and Waste Management, Department of Waste Management

Nußdorfer Lände 29-31, A - 1190 Vienna, Austriae-mail address: "Dr. Tanja Gomiscek" [email protected]

fax number 00 43 1 318 99 00 50

IntroductionOne of the greatest difficulties in recultivation of landfills is lack of the water available to plants. Since these plants are dependent on precipitation alone to fulfil their water requirements, it is necessary to utilise a substrate that can retain moisture over longer time periods and to make water available to the plants. The purpose of revegetating the landfill cap with fuel plants is to reduce the amount of precipitation that could penetrate into the landfill body.The types of fuel plants used in the study were annuals and perennials plants with proven high yields under Central European climatic conditions, whose biomass can be used for energy production. Such plants utilise stored solar energy as their fuel source.In this contribution results of the research work dealing with the recultivation with CO 2-neutral fuel plants on substrates comprised of residual waste materials (e.g. bio-compost and solid waste sludge compost) will be discussed. Particular attention is paid to the impact on the leachate minimisation.

Material and MethodsFour plants ( Populus, Miscanthus “Giganteus“ (C4 - Plant), Polygonum sachalinense and a grass mixture ) and five substrate combinations in five repetitions were set up for the bench vessel test. All together 115 plastic rain containers each of 200 liters were used as test vessels including uncultivated vessels for control. The investigated substrate combinations were the following: solid waste sludge compost and bio-waste compost in the ratio 40% to 60% to soil and vice versa as well as pure soil. Several times during the year the leachate of each vessel was collected individually, measured and analysed. During the investigation period the meteorological data were monitored and the evapotranspiration was calculated.

Results and DiscussionThe performed bench vessel test gave very good dry meter yields for all plants. The better growth rates were obtained on substrate combinations in the ratio 40% compost to 60% soil than in the ratio 60% compost to 40% soil for both compost arts, solid waste sludge compost as well as bio-waste compost. During two years of investigation leachate of each vessel was collected and analysed three times.


To get more information about the behaviour of leachate of distinct substrates the water retention capacity of each substrate and the plant available water were examined. Further the leachate amount of various substrates and various plants was investigated. Figures 1 and 2 show the comparison of leachate amount between a cultivated and an uncultivated variation during the investigation period.A significantly higher amount of the leachate on uncultivated variations was determined.

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Figure 1: The amount of leachate in l/vessel of Miscanthus

Figure 2: The amount of leachate in l/vessel of uncultivated vessels

Figure 3 shows the amount of leachate for different plants on various substrate combinations during one year, expressed in percentage (%) of the total precipitation quantity.

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Figure 3: The amount of the leachate for different substrate combinations and different plants in % of the total precipitation

The amount of the leachate of uncultivated vessels was much higher than of the cultivated ones - the difference was between 25% and over 50%, depending on compost mixture and type of the plant.

ConclusionsThe study showed that a use of proper material can minimise the leachate. Even better results were obtained with an optimal combination of quickly grown plants and compost substrate due to higher water retention capacity and plant available water conditions as well as exceeded evapotranspiration.

Abstract proposed to theIntercontinental Landfill Research Symposium, 14

Luleå, December 11-13, 2000

Contact: Dresden University of Technology, Institute of Waste and Site Management,Pratzschwitzer Straße 15D – 01796 PirnaPhone: +49 3501 530021 / 530025Fax: +49 3501 530022Email: [email protected]

Helga Grischek, Bernd Bilitewski:

Landfills flooded by Acid Groundwater - Acid Buffering and Heavy Metal Release A considerable number of MSW landfills in East Germany is situated areas of former open pit lignite mining. Owing to the up-rise of the groundwater those landfills are being flooded gradually. The groundwater is acidic (pH 5,0 – 3,0) and contains high concentrations of iron compounds and sulphate due to pyrite weathering processes in the overburden dumps.The MSW landfills were constructed without barriers to the subsoil. They contain municipal solid waste, industrial waste, demolition waste and mostly high amounts of lignite ashes from power stations. The majority of the landfills are small and were closed in 1990, but several were used until the end of the nineties.It is hardly possible to rehabilitate flooded landfills and consequently it is necessary to answer the following questions: What emissions (gas and leachate) can be expected from flooded landfill compared to unsaturated

landfills? Are acidic conditions to be expected in a flooded landfill due to the inflow of acidic groundwater? If acidic conditions are reached, will a considerable release of heavy metals occur?These questions will be answered on the basis of LSR (Landfill Simulation Reactor) test sequence and pHstatic elution tests. The LSR test is a useful method to investigate the emission behaviour of waste samples under the conditions of flooding. With the aid of a series of pHstatic elution tests the acid buffering properties and the Acid Neutralization Capacity (ANC) of waste samples (fresh and old) and single waste components (lignite ash, construction waste, organic material) were investigated. The heavy metal release from the samples under acidic conditions was measured.The gas and leachate emissions from a flooded landfill depend mainly on the temperature and on the substance influx with the groundwater. At temperatures below 15 °C no considerable gas emissions will occur. The organic emission potential is preserved and would be released, if the temperature in the flooded landfill rose up to values > 20 °C. The leaching of the landfill is intensified due to water saturation. It can be summarized that only a re-warming of a landfill (for instance due to warming-up of the mining lake) could cause high gas and leachate emissions.The ANC of waste samples (fresh and old waste) and single waste components (lignite ash, construction waste, organic material) varies over a wide range. Lignite ash appeared to be the most important buffering substance with ANC values of 7,000 meq/kg DM for fresh ashes and 5,000 meq/kg DM for an 8 years dumped ash. While fresh waste and organic material had very low ANC < 1,000 meq/kg DM, old waste samples and construction waste showed ANC values up to 2,500 meq/kg DM. It can be stated that the acid buffering properties of a landfill depend quite strongly on the ash content within the deposited material.The release of earth alkali metals and heavy metals in the pHstatic experiments increases with decreasing pH. While Ca and Mg are considerably released at pH values smaller than 7,0; Al and Fe will be released only at very low pH levels < 4,0. The release of Zn, Pb and Ni starts at pH 7,0 and increases considerably with decreasing pH.


Apart from the pH environment, the heavy metal release of a flooded landfill depends also on the redox potential. Under reducing conditions, and in the presence of sufficient amounts of sulphur, heavy metals are bound as sulfides. Metal sulfides have a very low solubility even under strong acid conditions. However, their oxidation by free or bound oxygen from the groundwater would cause a breaking-up of the sulfidic bonds. Heavy metals would be transformed into less stable carbonate or hydroxide forms and released. Conditions for metal sulfide oxidation and subsequent release of heavy metals from a flooded landfill are estimated. The possibility for acidification of flooded landfills and the effects of earth alkali and heavy metal emissions on the water quality of the surrounding mining lake are assessed for defined compositions of dumped waste, and for several ash contents. The assessment is based on a groundwater model, monitoring data and geochemical estimations.

LANDFILL STABILISATION IN A GENERATION? 15

Dr Jan Gronow Landfill Policy Manager

Environment AgencyRio House, Waterside Drive, Aztec West,

Almondsbury, Bristol BS32 4UDTel: +44 1454 62 4079 Fax: 62 4470

e-mail: [email protected]

Abstract

In 1994 the concept of landfill completion was introduced into waste management

regulations in the UK. Operators are no longer able to surrender their site licences until

regulators are satisfied that the condition of the site is such that it is unlikely to cause

pollution. Before surrender, the operator is responsible for the maintenance and

monitoring of the site and any pollution that the site might cause. Guidance was provided

to regulators on how to interpret completion and it was estimated that the time for a

household waste site to reach completion was likely to be greater than 100 years.

In order to accelerate stabilisation, the concept of the bioreactor landfill was advocated but has only been taken up in a few landfills and then only partially. The reason for this is explored. The Agency’s attitude to the interpretation of completion has developed since 1994. It is now considered that, once active control systems have been switched off, then if emissions are not unacceptable (a legal term) and are unlikely to increase, then surrender of the licence can be accepted. The determination of what is acceptable is not easy but not impossible.

However, the determination of the likelihood of increased emissions depends to a considerable extent on a knowledge of the degree of waste biodegradation that has occurred. Probably one of the best ways of ensuring that the majority of the waste in a site has the opportunity to degrade, is to operate the site using bioreactor techniques and to monitor emissions regularly until they start to decrease. Although the criteria for determining landfill completion have been relaxed somewhat since 1994, achieving them within the time-span of a generation (say 30 years) still depends on accelerating the stabilisation of the site. It has been suggested that achieving landfill completion within a generation desirable and is a definition of sustainable landfill. This will be discussed.

16EMISSION MEASUREMENTS AS A TOOL TO IMPROVE METHANE EMISSION ESTIMATES

H. SCHARFF *, H. OONK@ AND A. HENSEN #

* Afvalzorg Deponie bv, P.O.Box 6343, 2001 HH Haarlem, The Netherlands

tel: ++31 23 5534 322; fax: ++31 23 5534 544; e-mail: [email protected]

@ TNO-MEP, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands

# The Netherlands Energy Research Foundation (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands

ABSTRACT

Due to a successful national waste management policy the amount of organic materials processed on Dutch landfills has significantly decreased. At the same time the composition of the waste has also changed. Waste nowadays contains less biodegradable material and less moisture. This most likely reduces the amount of methane that is produced per tonne of organic material. Application of the IPCC-methodology to quantify national methane emissions from landfills probably will overestimate future emissions in the Netherlands. Consequently the emission reduction achieved in the period 1990-2010 as a result of current waste policy could be underestimated. The Dutch government could benefit from better methods to quantify the methane emission of Dutch landfills.

However, using other methods than the ones defined by IPCC to quantify methane emissions, is only allowed under certain conditions. To name a few: The method should be based on a larger number of real-scale observations. Emission

measurements can play an important role in this, on the condition that they provide an accurate impression of average annual emissions.

The consequences of the improved insights should be used to reconsider 1990-emissions (base-line correction). This can have implications for the way emission measurements should be performed.

Afvalzorg as landfill operator by means of an ISO 14001 certified environmental management system has committed herself to quantify the emissions of her landfills and where possible to reduce the emissions. As a part of certification, Afvalzorg, in co-

operation with ECN, has carried out methane emission measurements since 1997 (using mobile tunable diode laser, TDL). The data were compared with the landfill gas production model data. The results will be presented in the paper and will be a basis for discussion on (i) the validity of existing models for landfill gas generation and methane oxidation and (ii) how emission measurements can contribute to improved methane emission estimates.

The Afvalzorg/ECN measurements indicate that landfill gas formation on Dutch landfills might be reduced, compared to the situation ten years ago. They also support the observations of numerous reseachers (e.g. Czepiel, Boeckx, Christophersen & Kjeldsen, Maurice & Lagerkvist), indicating that seasonal variations have a major impact on oxidation and the average annual methane emissions.

In a study carried out by Afvalzorg/ECN/TNO for the Dutch government with respect to measurement methods several prerequisites are defined to ensure to a proper contribution to national emissions estimates. The method should be relatively cheap and able to deal with spatial and temporal variations of landfill gas emissions. It is argued that integral measurements of a large part of or a whole landfill should be performed for longer periods (1 to 3 weeks) and several times per year (preferrably in all four seasons). Carbon dioxide emissions should be monitored as well, since methane and carbon dioxide emissions give an improved understanding in the relative contribution of landfill gas formation and methane oxidation to methane emissions. This is of utmost importance when thinking about base-line correction.

Between 1997 and 1999 Afvalzorg and ECN have used a sophisticated method (mobile TDL) to determine methane emission estimates. An important drawback of this method is that measurements takes place on one day and therefore do not allow the evaluation of diurnal or seasonal variations. The advantage of both the mobile TDL method as well as for example the long path Fourier transform infrared (FTIR) spectroscopy method is that emission levels derived with these methods do take the spatial heterogeneity of methane emissions into account. However because of costs it would not be realistic to expect landfill operators to generate reliable average annual emission estimates with these methods. In the study mentioned above the mass balance method and a stationary plume method (based on collection of gas samples) have been identified as most practical to fulfil the requirements related to costs and spatial and temporal variations of methane emission. These methods will be elaborated as a sequel on this study. This summer both systems will be tested on a landfill site. The results of this sequel will be available in December 2000 for discussion on the Intercontinental Landfill Research Symposium.

17

Pesticides in solid waste leachate in Norway

K. Haarstad and T. Mæhlum

*Jordforsk, Centre for Soil and Environmental Research

N-1432 Ås, Norway

Abstract

It is generally assumed that landfills contains pesticides, at least in areas with a large

agricultural production, or near pesticide production sites or retailers. There are about 200

active municpal landfills, but in total more than 3000 sites have been registrered in

Norway. The total sale of pesticides amounted to 955 ton active ingrediences pr. year in

1998, of which 68 tons, or 7%, included compounds that are not related to agricultural

activities. There are about 120 approved active ingredients in pesticides sold in Norway.The pesticide concentration in the leachate will generelly depend on adsorption and degradation

inside the waste body and in the leachate, which again depends on the waste characteristics, the

management of the landfill, climate, topography and geology of the site. Also the content and type of

collodial matter and suspended particles in the leachate are important, and pesticdes have been reported to

be associated more with collodials mobilized shortly after precipiation events. In the liquid phase the

content and type of organic matter may significantly influence the fate of pesticides.

There are relatively few reports on pecticide concentrations in leachate. Leachate

samples from a waste disposal site in Switzerland showed concentrations up to 124 g/l

of mecoprop, and downgradient groundwater with surpricingly high conentrations up to

975 g/l (Zipper et al., 1998).

In a testing program for leachate characteristics in Sweden, it was found that 5 out

of 8 leachate samples contanined residues of phenoxy acid herbicides, and only one

sample out of 20 of leachate particles contained pesticide residues. Analyses of leachate

samples from a landfill in Denmark showed few detecionts of pesticides.

Here we summarize findings of pesticde residues in leachate samples from 3

major active Norwegian landfills, before and after leachate treatment. The analyses

represents grab samples taken both before and after leachate treatment.

Table @. Pesticides and metabolites included in the analyses.Pesticide Type logkow pKa Sol. (mg/l) pol. Mol. Location Class

2,4-D H 2.7 2.64 311 - 221 be aryloxyalcaonic acid

atrazin H 2.5 1.7 33 - 216 fw 1,3,5-triazin

bentazon H 5.84 3.3 570 - 240 bes, h,ww,fw -

cypermetrin-alfa I 7 0.01 416 pyretroid

cyprokonazole F 2.9 93 azole

DDT I 0.001 0 354 f organoklorin

diazinon I 3.3 60 304 organic P

dikamba H 3.98 1.87 6.5 - 221 benso-syre

dikloroprop H 1.77 3 350 - 235 bes, h, ww aryloxyalkonic syre

dimetoat I 0.7 23 229 fw organic P

endosulfan I 4.7 0.3 407 organic Cl

esfenvalerat I 6.2 0.002 420 pyretroid

fenitrotion I 3.4 21 277 organic P

fenpropimorf F 2.6 6.98 4.3 + 304 b, f morfolin

fenvalerat I 5 <0.010 420 f pyretroid

fluazinam I 465 2,6dinitroanilin

fluroksypyr H -1.2 2.94 91 - 255 aryloxyalkonic syre

ioksynil H 3.96 50 - 371 OH-benzonitril

iprodion F 3 13 330 f dicarboximid

klorfenvinphos I 3.85 145 360 org.fosfor

lindan I 7 291 f org.klorin

linuron H 3 81 249 ww urea

mankozeb F 1.75 <<0 8.4 279 h, ww, fw acylalinin

MCPA H 2.75 3.07 734 - 201 be, h, ww aryloxyalkonic acid

mekoprop H 1.29 3.78 860 - 215 bes, fw aryloxyalkonic acid

metalaksyl F 1.75 <<0 8.4 279 h, ww, fw acylalinin

metamitron H 0.83 1.7 202 ww 1,2,4-triazinon

metribuzin H 1.58 1 214 h, ww, fw 1,2,4-triazinon

penkonazol H 3.72 1.51 73 - 284 azole

permetrin I 6.1 0.2 391 pyretroid

pirimikarb I 1.7 pkb 3000 + 238 carbamat

prokloaz F 4.38 3.8 34 - 377 azole

propaklor H 2 613 212 ww kloracetanilide

propikonazol F 3.72 1.09 100 - 342 fw, f azole

simazin H 2.1 pkb 6.2 - 202 1,3,5-triazin

tebukonazol F 3.7 32 308 azole

terbutylazin H 3.04 pkb 8.5 - 230 1,3,5-triazin

tiabendazol F 4.73 30 (ph 5) - 201 e, fw benzimidazole

vinklozolin F 3 3.4 286 dicarbox-imid

Location: b=bølstad landfill, e=Esval landfill, s=Spillhaug landfill, f=forest production landfill,

fw=farmland well, ww=water work

Results and discussion

Leachate samples with positive detection of pesticides have concentrations between 0.03

– 30.01 g/l (Table @). Some substances have detection in all samples, such as the

phenoxy acids mecoprop and dichloroprop, and bentazone

Table @. Pesticides (g/l) found in MSW leachate samples in Norway

B=Bølstad, E=Esval, S=Spillhaug Landfills

Table @. Pesticdes (maximum conentrations) found in leachate or leachate polluted groundwater at waste

sites in the forest trees nurseries (g/l)

18Ketil Haarstad & Trond Mæhlum

Jordforsk, N-1432 Ås, Norway

The use of Chloride concentrations for estimating dilution in aerobic leachate treatment systems

Cl represents about 0.2% of the in situ mass of refuse, and typical Cl concentrations in leachate in

Norway varies from 90-3000 mg/l, while measurements from UK shows variation between 500-5000 mg/l.

Cl is considered as a conservative (non-reactive) anion and is often used as a tracer in water transport

experiments and studies. Extensive leachate treatment systems based on holding dams, aeration ponds,

phytotreatment and filtration experience show Cl reduction in the range of 30-55%, of which the aerobic

step constitutes more than 90%. Typical sizes of the aeration pond of leachate treatment systems in Norway

is 2000-4000 m3, with a corresponding mean hydraulic retention time of 20-40 days, and a mean hydraulic

loading rate (HLR) of 40-80 mm d-1 (Mæhlum and Haarstad, 1997). If the reduction of Cl in treatment

systems is caused by dilution, this has to be corrected for when calculating the reduction of pollutants. The

hydrological budget, including precipitation, evapotranspiration, surface runoff and groundwater transport,

can not explain the high reduction rates of Cl in most cases. If, on the other hand, Cl is removed from the

aqueous phase, correction due to dilution is not necessary. The objective here is to simulate aerobic

treatment to investigate if the field reduction rates can be duplicated in the laboratory, and to see if there are

some physical or chemical factors that significantly influence this reduction.

The experiment used 3 real leachates and 8 artificial leachate samples with

varying concentrations of Cl, organic C, Tot-N and Fe in addition to 3 control samples.

Leachate samples were collected from two landfills with municipal solid waste (MSW).

The oxygen consumption in the leachate samples was considerably lower than in the

artificial samples, probably due to inhibitory compounds in the leachate. Mean Cl

reduction was 22% for the leachate samples, 46% in the artificial samples and 10% in the

controls. Only TOC concentration had significant influence on the oxygen consumption

in the respirometer, both when measured in the artificial samples (p< 0.036) and for all

samples (p<0.013). Oxygen consumption was the only significant factor (p< 0.0079) for

Cl reduction. Centrifugation showed no significant effect on Cl reduction. The reduction

of Fe was low in the experiment, but was strongly influenced by centrifugation. Also the

reduction of TOC and N was influenced by centrifugation. The reduction of Cl in aerobic

treatment may be dependent on the formation of particles.

195701 Este Avenue 5701 Este Avenue 1847 Whittaker Hollow Rd. Cincinnati, Ohio 45232 Cincinnati, Ohio 45232. Blacksburg, Va. 24060(513) 641 5500+19 (513) 641 5500+18 (540) 552 3684fax (513) 482 7967 fax (513) 482 7967 fax (513) 482 [email protected] [email protected] [email protected]

Gary Hater and Roger Green both intend on coming to the conference, Gary Hater will be the presenter.

Analytical Measurement of Carbon and Nitrogen Cycles in Landfill Bioreactors

Gary R. Hater Roger B. Green C. Douglas Goldsmith Ph.D.Waste Management Inc. Waste Management Inc. Alternative Natural Technologies

Waste Management Inc. is implementing a bioreactor development program. Evaluating the relative merit of the different operating variants of bioreactor technology is one of the program’s major initial objectives. Fifteen large-scale (>200,000 m3 each) demonstrations are planned to be underway at the company’s landfills by the end of 2001 to accomplish this.

A focus of the sampling and analysis program for these demonstrations is to understand carbon and nitrogen cycling in solids, liquids, and gases of the landfill system. Accordingly, extensive sampling of waste, leachate, landfill gas, and surface emissions is being performed. Commercially available as well as research methods of sampling and analysis are being employed. Waste analyses include density, moisture, volatile solids, settlement, biochemical methane potential, cellulose, lignin, pH and inorganic nutrients. Leachate analyses include COD, forms of nitrogen, inorganic nutrients, pH, and phosphorus. Gas monitoring includes landfill gas and non-methane organics (NMOCs). Surface emissions testing and analyses include methane.

These are the methods, sampling tools and techniques have been selected to date. As the demonstrations progress and data are collected, the costs and benefits of each of these methods will become better understood and modified. Several unique techniques have been used to date. Bucket augering followed by obtaining weights of known volumes has been used for calculating the densities of waste mass. A global positioning system is being used to estimate waste mass density. Available nitrogen and phosphorus measurements in the waste are worth further collection and evaluation. Other areas under consideration for future study include identifying improved gas and emission sampling and analysis techniques, reducing the frequency of waste sampling, and refining the leachate parameters list.




20Results from A Large-Scale Aerobic Landfill System

Mark Hudgins, Environmental Control Systems, Inc., Aiken, South Carolina (USA)Leon Green, Environmental Control Systems, Inc., Aiken, South Carolina (USA)

AbstractUnder anaerobic conditions, slow stabilization of the waste in a landfill produces methane, (an explosive, “green house” gas) and contaminated leachate over long periods of time. Moreover, many of the compounds found in landfill gas (LFG) are considered “green house” gases which may contribute to global warming. In attempts to reduce the production of this leachate, composite soil cap systems are constructed over landfilled waste. Additionally, many landfills use sophisticated subsurface liner and leachate collection systems to reduce the release of leachate into the environment. However, these cap, liner, and collection systems ultimately fail, potentially releasing methane gas and leachate to air and groundwater. As a result, this design approach only postpones the inevitable risks associated with landfills.

Building on the results of recent field-scale aerobic landfill projects, a 7-acre aerobic landfill is currently operating in Tennessee (USA). Although the benefits of aerobic degradation of MSW within a landfill include 1) an increased rate of waste decomposition and settlement, 2) reduced levels of contaminants in the leachate, and 3) decreased production of methane (over 90%), the primary goal of this project is to eliminate the offiste disposal of leachate, currently at a rate of over 160,000 gallons per month, via the evaporative effects created in the landfill. This paper presents the results of this project to date and future application at this landfill.

Further, combining these benefits with the possibility of landfill reuse (via landfill mining) could increase the potential for a sustainable landfill strategy to lower overall landfill operating costs, reduce environmental risks, and significantly extend the life of landfills worldwide.

21Methane Oxidation in Optimised Landfill Cover Layers

under Different Seasonal Conditions

Marion Humer, Peter Lechner

Universität für Bodenkultur Wien (University of Agricultural Sciences, Vienna)IWGA, Department of Waste ManagementNußdorfer Lände 29 - 31, A-1190 Vienna

Tel.: ++43-1/ 318 99 00 -44Fax.: ++43-1/ 318 99 00 -50

e-mail: Marion Humer<[email protected]>

Uncontrolled emitted landfill gas contributes to the greenhouse effect due to its high content of methane. Worldwide about 40 million tons of methane result from waste landfills. Methane emissions from waste landfills are situated at third rank of anthropogene methane sources. These emissions are mainly caused by inadequate gas collection systems and uncontrolled emissions from old dumps and unauthorised open dumping. With traditional gas collection systems only 40 to 60 % of the produced gas can be collected and reused or safely disposed of.

A low-cost alternative or an additional measure to the conventional methods is the use of suitable landfill cover layers, e.g. made of compost, which provide appropriate conditions for microbial methane oxidation. We received promising results from laboratory tests with soil columns filled with municipal solid waste compost and sewage sludge compost. Different test series were carried out in an air-conditioned chamber to examine the methane oxidation potential at various temperatures, with various water content and methane supply. These results are now reviewed in a large-scale outdoor experiment, which began last year. On a landfill for household waste in Lower Austria several test cells with compost materials of different thickness and composition has been installed. The various landfill covers are designed like vast biofilters.

The previous results from our experiments show that mature, well decomposed compost substrates support appropriate conditions for microbial methane oxidation particularly under outdoor conditions. Methane-oxidation rates in compost materials are clearly much higher than those in natural soils and traditional landfill cover soils. Also under winter conditions high methane-oxidation rates were achieved in compost substrates. The data from the differently designed test cells show that it is very important to install a gas distribution layer below the compost cover and to dimension the thickness of the compost cover conveniently, in order to reach homogenious and efficient methane oxidation.

The data from these investigations and particularly the results from the field experiment on the landfill as well as the technical design of a landfill cover layer, which is capable of reducing methane emissions, will be presented.

22MSW landfill leachate: Present and future composition

Kjeldsen*, P.; Barlaz, M.; Rooker, A.; Ledin, A.; Christensen, T.H.

*Corresponding authorDepartment of Environmental Science and EngineeringTechnical University of DenmarkDK-2800 LyngbyDenmarkFax: +45 45932850E-mail: [email protected]

IntroductionThe high number of cases of groundwater pollution at landfills and the substantial resources spent in remediation suggest that landfill leachate is a significant source of groundwater pollution. Landfill leachate from municipal solid waste landfills contains a variety of different pollutants (dissolved organic carbon, inorganic salts, heavy metals, and xenobiotic organics). Many investigations of the composition of landfill leachates have been presented giving a picture of typical present composition of landfill leachate. However this data only represent the initial 10-30 years of the lifetime of landfills. Most of the investigated landfills are in the methanogenic phase, and almost no data exists for the following phases where the methane production is ceasing. It has been hypothesized that the pollutant release from landfills in the mature phases might increase substantially due to oxidation processes.

The objective of this paper is by review of the literature to give an overview on typical present leachate composition, and to present and discuss hypothesis for the evolution of landfill leachate composition through the future landfill phases based on model considerations and laboratory experiments.

Present leachate compositionA typical decreasing concentration trend with time is observed for most of the pollutants observed through the initial acidogenic and methanogenic phases. The dissolved organic matter (measured as COD or BOD) seems to reach more stable concentrations, and the ratio BOD/COD is typical around 0.10 for methanogenic phase leachate. Nitrogen typical present as ammonia is not decreasing as much with time, and typical values in the order of 200-800 mgN/l are observed. The heavy metal concentrations are very low, and landfill mass balances show that only a small fraction of the heavy metals originally contained in the landfilled waste has been leached out. A large variety of xenobiotic organics have been observed in landfill leachate with very broad concentration ranges.

Future landfill phases and consequent leachate composition

The landfill is postulated to undergo several degradational phases following the methanogenic phase. When the methane production gets low, air starts to significantly intrude the uppermost part of the waste (Air intrusion phase). After a further decrease in methane production the oxygen is intruding the upper waste layers and is primary used for oxidation of the methane transported to the top of the waste layers (Methane oxidation phase). When methane production becomes insignificant the oxygen is used for oxidation of solid organic matter and reduced inorganic species (such as metal sulphides) follow by production of carbon dioxide (Carbon dioxide phase). Due to the oxidation of insoluble metal salts and the degradation of solid organic matter serving as a sorptive capacity for metals, the metals are potentially released to the environment. A few laboratory experiments have been carried out to study the behaviour of metals in old waste samples (taken from landfills) under oxidising conditions. Most of the studies indicates that other attenuating reactions take over when the sulphides and solid organic matter are oxidised, and enhanced

Peter Kjeldsen, 01/03/-1,

Can we think of a better title implying the words: composition, landfill, leachate, MSW, stabilization


releases of heavy metals in this phase seems not to take place. More research is, however, needed to back up these initial findings.

23

Use of LCA approaches for optimising mechanical-biological pre-treatment and landfilling of residual wastes M. Koller, K. Soyez, Centre for environmental studies, Universität Potsdam, Germany.

Matthias Koller, Zentrum für UmweltwissenschaftenUniversität Potsdam, Park Babelsberg 14, D-14482 PotsdamGermany

Phone: +49-331-9774447, Fax: +49-331-9774433Email: [email protected]

The paper shows how LCA approaches can be used for optimising mechanical-biological pre-treatment and landfill of residual wastes. As there is a wide variety of waste treatment options within the mechanical biological pretreatment and landfill of residual wastes, decision tools are needed to identify the environmentally best option. For this purpose the authors developed a computer aided assessment tool for integrated waste systems (CUBIS). The presentation shows interim and final results of ongoing investigations.

Emphasis is put on identifying optimisation potentials (see fig 1) and weak points by application of a thorough sensitivity analysis including all important model parameters and assumptions. Among others the influence of waste properties and amounts, process design and efficiency, separation rates and recovery efficiency and the background infrastructure, in which the waste management system is embedded in are demonstrated and discussed. Based on this results hints for the optimisation of waste management systems and for the application of LCA within the decision making process are given.

t Fig. 1: Optimisition potential for the waste air treatmen

Fig. 2: Influence of Composting duratino and landfill methan oxidation on the overall result of GPW

With respect to the landfill, the influence of the most important landfill parameters on the overall results of the LCA are discussed. This includes the amount and composition of gas emissions and leachetes, the methan oxidation capacity, the lecheate treatment system, the capital burdens for constructing and maintaining the landfill, the buffer capacity for heavy metals, the time frame, over which the landfill is to be considered. A special emphasis is laid on the discussion of the interaction between the pretreatment and the landfill with respect to the total environmental burdens and benefits (see fig. 2). It is shown, that both systems shouldn’t be optimised individually but in a holistic approach optimising the results of the total

systems. The presentation shows, how the optimum stabilisation duration can be deteremined in dependency from the methan capacity of the landfill and/or the energy demand of the pretreatment.

The results show, that the environmental impacts of landfills can be reduced to more than 90% by mechanical – biological pretreatment. The specific contributions from the disposal of residual waste amounts to less than one percent of the national inventory (fig. 3).Through extensiv material and energetic recovery (fig. 4) the disposal of residual wastes may even lead to environmental benefits in the overall results.

Fig. 3: Specific contributions of different waste treatment systems

Fig. 4: Potential of material and/or energetic recovery

The final conclusion is that there is no generally best waste management system as the results, i.e. the potential ecological impacts of a given system fairly depend on site and case specific conditions. The waste management systems should therefore be designed with consideration of its integration into the local and regional infrastructure.

24Could there be Three Rate-Limiting Steps in Solid-State Digestion?

Duncan J Martin, Department of Chemical Engineering, National University of Science and Technology, PO Box AC939, Ascot, Bulawayo, Zimbabwe.

[email protected] or [email protected]

Tel 00263 91 239 833 (roaming mobile)

===#===

A rate-limiting step is generally understood to be unique, the slowest in a sequence of steps. However, in a complex and long process, various steps might be limiting at different stages. Moreover, the rate of any step might be reduced by inhibition or by spatial restriction, so a potentially fast step could be rate-limiting in practice. A new model of SSD proposes that just such conditions obtain in landfills. This paper will expand on the proposed mechanisms underlying the model and the experimental evidence available in support of it.

Rapid aerobic then anaerobic metabolism create highly acidic conditions soon after the placement of richer wastes. This preserves the waste in a state resembling silage, in which further reaction is prevented by inhibitory conditions. Stabilization at any point commences only with the arrival of a very slow-moving reaction front. Ahead of it, all reaction is under profound acid inhibition; behind it, acid inhibition is absent. All the readily-degradable organic matter (RDO) is consumed here, creating a sharp transition from highly acidic raw waste to depleted waste. This primary degradation process is thus tightly localized. The first three reaction steps (hydrolysis, acidogenesis and acetogenesis) occur in a thin, acidic layer at its leading face However, the final step, methanogenesis, occurs under milder conditions at the trailing face, in a distinct inner layer. This is separated from the outer layer by a reaction-free buffer layer, thick enough to protect methanogenesis from inhibition.

The degradation of any LDO (less-degradable organic matter) mixed with the RDO is also delayed until the reaction front arrives. It then proceeds as a secondary, dispersed process, which reaches completion some time after the reaction front has passed. Proceeding free from inhibition and in a growing volume, it might reach completion within a few months or less, even for the most recalcitrant substrates. In contrast, the primary process is retarded by acid-inhibition and by localization in a slower-growing volume. Paradoxically, the degradation of ‘readily-degraded’ material is rate-limiting!

Each viable seed particle surrounded by RDO initiates a roughly spherical, independent micro-reactor, bounded by a reaction front. This relieves acid inhibition as it advances. In a large mass of LDO, in contrast, there is no ‘ensiling’, so no relief of acid inhibition is needed. The primary process is therefore by-passed and the secondary process commences immediately. However, this route might be rare, as lean wastes are liable to acidification by diffusion from rich material nearby. Thus, a mechanism based on expanding micro-reactors has the potential to dominate the landfill process.

Acetogenesis probably controls the rate of expansion. It may be rate-limiting for decades if the more widely-spaced of the viable seed particles are far apart. However, mass transfer processes might control an initial ‘seed maturation’ stage, while hydrolysis almost certainly controls the final stages. Notably, methanogenesis is never directly rate-limiting. Immature seed particles cannot develop in waste saturated with inhibitory volatile fatty acids. Moreover, small particles are soon inactivated by inward diffusion of VFA, so there is a minimum viable size. Larger particles, however, can utilize VFA as fast as it diffuses in. Although the outer parts of such a particle are subject to inhibition, they act as a buffer layer, protecting a deeper methanogenic layer. Methanogenesis is therefore diffusion-limited at this stage.

Seed maturation relieves this limitation. If the methanogen population in a seed particle is low, the buffer layer must initially be quite thick, so that both the concentration gradient and the VFA flux are low. However, as the methanogens multiply, methanogenic activity gradually advances, thinning the buffer layer. Diffusion accelerates. So does methanogenesis – but only because it has more substrate. Of course, methanogenesis does determine the length of the maturation stage (as the sensitivity of the methanogens to inhibition controls the rate of their growth into the buffer layer) and the critical size of seed particle – but such indirect effects are not strictly rate-limiting.

Maturation may take a few days or many months, depending on particle size and methanogen population density. (This is no doubt why digested waste is such an effective seed for engineered digesters.) It ends when the concentration gradient is steep enough to relieve acid inhibition slightly at the seed surface. The reaction front then forms, initiating micro-reactor expansion. Acetogenesis now becomes rate-limiting.

Hydrolysis only becomes rate-limiting after the reaction front has traversed every part of the waste mass. However, if LDO stabilization is indeed completed soon after the front has passed, this final stage will occur only in the last zones to be traversed, so will be brief. If so, the typical long ‘tail’ in landfill data might be chiefly due to slow micro-reactor expansion into large zones that initially contained no viable seed particles. Thus, dramatic process acceleration could be obtained by controlled seeding.

DJM/22.4.00/Lulea Abstract.

25

Intercontinental Landfill Research Symposium,

Lulea University of Technology, Luleå Sweden December 11-13, 2000

Abstract___________________________________________________________________________________T. Marzi, S. Palitzsch, K. Keldenich, R. Kümmel

Factors and technical methods influencing the Quality of MSWI Bottom Ash

The Quality of MSWI-Bottom Ash is determined by the content of leachable salts and heavy metals. For using MSWI Bottom Ash, it is necessary to reduce the harzard potential of the ash. At the moment there are existing various technical processes to improve the quality. The processes can be distinguished in thermal (Melting and Sintering) and chemical-physical-processes (Leaching and Ageing). The various processes have different effects of the hazardous potential of MSWI Bottom Ash. To value this processes, economical and ecological criterias have to be considered.In this paper different processes are represented and the chemical and physical effects, which change the quality of the ash are discussed. Also a new investigated process, named „rapid ageing“ is discribed. This method is based to a process-integrated-treatment. Therefore a carbondioxide containing medium is used for carbonatisaton of the ash.The presented technical processes will be valuated about the attainable quality of the ash, the technical feasability and the costs. Therefore dates from literature and dates which descended from own examinations will be used.

Corresponding author:Dr. Thomas Marzi Fraunhofer-Institut für Umwelt- Sicherheits- und Energietechnik UMSICHT Osterfelder Straße 3 DE- 46045 Oberhausen, GermanyTel: +49(0)208/8598-230 Fax: +49(0)208/8598-290 email: [email protected]

26LFG emission measurements in arctic climatic conditions

Seasonal variations and methane emissions mitigation

Christian Maurice & Anders LagerkvistLuleå University of Technology

S-971 87 Luleå, [email protected], [email protected]

The Northern part of Scandinavia has a low population density, and the long distances between the cities lead to the construction of relatively small landfills where the waste degradation is slower due to lower temperatures. The estimation of LFG emissions from such landfills situated in arctic regions is more difficult because of the long winter period. The cold temperatures and the snow cover make both the measurement procedure and the estimation of LFG emissions more difficult.

This article presents results from 3 projects that were conducted at 3 landfills in Northern Sweden and Finland.

At the landfill of the city of Luleå, LFG emissions and temperatures in the top cover of a test cell were measured monthly during a one year period. During the winter, several strategies were tested to measure the LFG emissions.

At the landfill of the city of Umeå, the seasonal variation of the methane mitigation in a biofilter was investigated.

At the landfill of the city of Kemi the seasonal variations of the LFG emissions were investigated. The oxidation capacity if the soil was also measured in laboratory experiments.

The comparison between the alternative methods to measure LFG emissions when snow covers the soil surface, showed that the best way is to remove the snow and measure directly at the landfill surface. LFG emissions also occur through the snow cover but it is easy to disturb the LFG flow and measurements through the snow cover were therefore abandoned.

A seasonal variation of the quality of the emitted LFG could be observed i.e. methane emissions occured during the winter period while most of the methane was oxidised during the summer period. Such patterns were observed at the landfills at both Luleå and Kemi.

During the late summer, methane emissions could also observed when the soil dried. The phenomenon occurred in the biofilter at Umeå but could also be observed at the landfill at Kemi.

The efficiency of methane oxidation is believed to at the origin of the variation of the methane emissions. During the winter, the upper par of the landfill cover freezes, and the



microbiological activity is reduced. The formation of an ice layer on the top of the soil surface could also influence the LFG emissions. The oxidation capacity of the soil was tested in the laboratory to compare it to the emission levels measured in the field.

27Abstract submittal

Authors Satoshi Mizutani (corresponding author), Shin-ichi Sakai, Hiroshi TakatsukiAffiliation Environment Preservation Center, Kyoto UniversityAddress Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501 JapanTel: +81-75-753-7711Fax: +81-75-753-7710e-mail: [email protected]

Title and abstract

Acid neutralizing capacity (ANC) and leaching test scheme for short and long term behaviour of granular waste

The behaviour of heavy metal leaching from some granular waste, such as municipal solid

waste incineration residues, their chemical treated ash, contaminated soils, coal fly ash, electric

furnace dust and saw dust of preservative treated wood, have to be checked before landfill in

order to prevent environmental pollution. Although various leaching test methods are proposed,

the universal method are not determined yet. In this paper, a leaching test scheme composed of

two-stage serial batch test for short and long term leaching behaviour are proposed.

In first, Japanese standard leaching test (JLT-13), pH dependent test and column test were

performed for MSWI residues and factors of determining metal leaching behaviour were

clarified. pH dependent test showed that the leaching quantity from wastes were controlled by a

final pH of the leachate. Column test gave the leachate of the initial stages in the landfill. The

leachate pH was controlled by the waste characteristics. Furthermore, ionic strength of the

leachate rose because soluble salts such as Na, Ca, Cl leached out smoothly. It will cause an

increasing of metal release.

Leaching test of which leachant is distilled water and small L/S , for example, JLT-13 in

Japan or CEN test in EU, which is becoming an European standard leaching test, are effective for

short term leaching behaviour evaluated in the conservative side. On the other hand, the waste pH

decrease with time by CO2 in the air or acid rain and lower the leachate pH in the long term. In

order to know the final pH of the waste after landfill, ANC (acid neutralizing capacity) of the

waste are focused on, as a pH controlling factor of the granular waste materials. Granular wastes

were titrated in the availability test, and they were classified based on the ANC and initial pH of

the waste. Because ANC of the materials are various, the final pH and metal leaching behaviour

are expected to be different.

Finally, leaching test scheme for short and long term assessment are proposed. The scheme is

composed of two stage serial batch tests. The first step is a single batch test of which leachant is

distilled water, L/S = 10 for 6 hours for short term behaviour. The second step is a single batch

test whose leachant is an acid for long term behaviour. This scheme is based on present Japanese

official leaching test or CEN Test, in the 1st step. Information about long term leaching behaviour

can be given from second step.

28Corresponding author:Åsa Mobergfms, Environmental Strategies Research GroupStockholm UniversityBox 2142S-103 14 Stockholm, Swedene-mail: [email protected]: +46-8-4023801

Environmental effects of landfilling of solid waste compared to other options – assumptions and boundaries in life cycle

assessment. G. Finnveden, J. Johansson, P. Lind and Å. Moberg

Introduction

In many countries, both energy systems and waste management systems are changing.

One driving force for these changes is the threat of climate change caused by emissions

of CO2 and other greenhouse gases. In discussions on waste management, a waste

hierarchy is often suggested. Although different hierarchies are suggested a common

feature is that recycling of waste is preferable over incineration which is preferable over

landfilling. In this study we have compared different treatment options for the

combustible and recyclable fractions of municipal solid waste. The aim has been to

identify advantages and disadvantages of different treatment methods and also to test the

validity of the waste hierarchy.

Methods

For the study we have used Life Cycle Assessment (LCA) methodology. Established

methods have been used for both the Life Cycle Inventory Analysis and for the

Characterisation. Weighting is performed using two different weighting methods.

The study is based mainly on Swedish conditions. In the base scenario of the study, the

assumptions made are that marginal electricity is produced from hard coal, avoided heat

production is from forest residues, transports are short and the time perspective is the

hypothetical infinite. Gas collected from landfills are used for heat and electricity

generation, and 50% of the landfill gas is assumed to be collected. Many of these

assumptions are altered in different scenarios to test the influence of varying conditions.


Results

With the assumptions of the base scenario the waste hierarchy is found to be valid for the impact categories total energy, greenhouse effect, photochemical oxidant formation, acidification, eutrophication, sulphur oxides, human toxicology and for total weighted results. For other impact categories, slightly different results are obtained. Considering non-renewable energy, abiotic resources and nitrogen oxides the ranking shows recycling to be preferred before landfilling, leaving incineration to be the least preferred alternative. The ecotoxicological impact category gives different rankings depending on which characterisation and weighting methods that are used. Different rankings within an impact category may also be found for separate fractions of the household waste.

A major reason for landfilling being ranked low is often that recycling and incineration with heat recovery produce products, either recycled material or heat, which can substitute other products. From landfilling, some landfill gas is collected, but in general less products are received.

In the study performed different scenarios have subsequently been analysed, altering some of the assumptions of the base scenario. Most relevant from a landfilling perspective are time aspects, application of the carbon sink concept and transportation issues.

Time perspectiveEmissions from landfills, as opposed to those from incineration and recycling processes,

are very much spread over time. When modelling a landfill different time perspectives

may give rise to different results. In the base scenario a hypothetical infinite time

perspective is used. This time perspective is defined by a complete degradation and

spreading of all landfilled material. We have also studied a shorter time period, called the

surveyable time period, corresponding to approximately 100 years. When a shorter time

period is used, landfilling appear as a more attractive option. Emissions of metals are

reduced as well as emissions of carbon from landfilled plastics. This leads to changed

rankings of waste management options for plastics regarding greenhouse gases, where

landfilling becomes the second best option and for the whole system for the category

ecotoxicological impacts, where landfilling is credited differently depending on impact

assessment methods used.

Carbon sink

With the shorter time perspective described above there is also a possibility to consider

the landfill to be a carbon sink. This assumptions applies to the part of the waste

containing biological carbon, which is not degraded and released to the atmosphere

during the surveyable time period. This carbon stays in the landfill, and may therefore be

considered to be withdrawn from the atmosphere. Applying this concept, the amount of

biological carbon withdrawn may be credited the landfill option as avoided CO2

emissions. In the study, this assumption leads to a result where the ranking of the

different options are altered for the impact category greenhouse effect, which also makes

out a large part of the total weighted impacts. The ranking becomes recycling preferable

to landfilling, which in turn is preferable to incineration for the total weighted values and

also, with a small difference between the last two, for the greenhouse effect category.

Transportation of waste

When comparing different waste management options it is also of interest to consider

differences in transportation demand between them. In the cases of recycling and

sometimes also incineration, the waste has to be separated into fractions and transported

by households to collection points. Distances to them and from them to the processing

facilities are compared to the distances to the landfills. In the study performed it can be

seen that the transportation to processing facilities by highway trucks are not making any

major influence on the results. Transport by passenger car may however give a significant

impact in some categories, mainly for photochemical oxidant formation, sulphur oxides

and toxicological aspects. The assumption that no transportation by passenger car is made

for landfilling, thus favours this option.

Conclusions

Depending on the way landfills are modelled and on the assumptions made for the system

under study, life cycle assessments may in some cases give results where landfilling is

preferred to incineration. In general, the most preferable option is recycling. It is

important to get more certain ways of modelling and assessing waste management

options to be able to get more reliable results.

29TREATMENT OF MSOR (MECHANICAL SEPARATION ORGANIC RESIDUES) IN A LANDFILL-BIOREACTOR

H. OONK* AND H. WOELDERS**

*TNO-MEP, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands

**Essent, P.O. Box 5, Wijster, the Netherlands

ABSTRACT

At Essent (previously known as VAM) waste treatment company in Wijster, waste is mechanically separated prior to treatment. One of the product streams is the mechanically separated organic residue (MSOR). Dutch legislation does not allow landfilling of MSOR after 2000, so bioreactor technology is considered for future treatment of this material. To evaluate this possibility, an integrated research programme is defined, consisting of lab-scale research, a full-scale demonstration and a desk-study.

For the full-scale demonstration, a 49.000 tonne demonstration cell was built in 1997 (constructional details were presented at Lulea, 1998) and methanogenic conditions were rapidly established after closure of the cell. The bioreactor demonstration is intensively monitored for the composition of the waste input, the emissions to air during construction, and the leachate and biogas production and quality during operation. Although leachate infiltration was hampered by the poor hydraulic conductivity of the waste, gas production from the MSOR is high: half time of biodegradation is about 2 years. Medio 2000 the test will is finished. Samples are drilled from the waste package and analysed for composition, remaining gas formation potential and leaching behaviour. Thus a check is enabled on material balances of a.o. organic carbon.

In order to explore the middle and long-term processes, lab-scale research was performed in addition. In this way insight is obtained in processes and emissions during bioreactor-treatment and quality of the MSOR after being stabilised and flushed.

The test-cel and its accompanying lab-scale research indicated that a bioreactor is a promising technology to treat organic residues with: a biologically stable residue; a high conversion of waste to energy, comparable to what can be obtained from

incineration with energy recovery; negligible emissions to air during construction and to soil and ground-water during

and after the construction period; an end-product with acceptable rest-emissions, which even may be suited for re-use

within existing legislation.

LANDFILL GAS EMISSION MEASUREMENTS 30 USING A MASS-BALANCE METHOD

H. OONK AND T. BOOM

TNO-MEP, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands

ABSTRACT

In the years 1993 and 1994 TNO measured methane and carbon dioxide emissions from about 20 Dutch landfills. The emissions are compared with expected emissions, as calculated using landfill gas formation models that are generally accepted in the Netherlands.

The results and conclusions of these measurements have never been published in some journal or presented at a symposium. For a number of reasons the measurements are of importance and therefore TNO wants to improve the accessibility of the results by publishing the results at Lulea.

Methane and carbon dioxide emissions were measured using a mass-balance method. The measurement equipment (sampling, analysis and data-acquisition) was fully automated and the emission measurements could be pertained for longer times (several weeks) at acceptable costs. For every landfill information was collected about amounts of waste, its age and composition, to enable a prognosis of landfill gas formation.

For each individual landfill, actual landfill gas formation is obtained from the sum of methane and carbon dioxide emissions and amount of landfill gas extracted. The actual landfill gas formation was generally in fair agreement with the landfill gas formation as calculated with the prognosis, so the measurements can be regarded as a confirmation of the existing landfill gas formation models.A comparison of the ratio of methane and carbon dioxide emissions with the ratio of methane and carbon dioxide concentrations in the extracted gas gave an indication about the degree methane oxidation. The result indicated that methane oxidation is most likely higher than the 10%-default as being used in the Dutch national estimate.

The results of this study are of importance, since the measurement results provide a relative large data-base of methane and carbon dioxide fluxes from landfills in a North-western European country shortly after 1990 (the reference year in the Kyoto Protocol) and just before waste composition drastically changed due to Dutch and European waste policy.

31

FULL SCALE PERFORMANCE OF BIOLOGICAL LEACHATE TREATMENT AT LOW TEMPERATURE

Pelkonen Markku 1) , Kotro Mikko 2), Wang Zengzhang 1)

1) Helsinki University of Technology, Laboratory of Environmental Engineering

PO BOX 6100, FIN-02015 HUT (Espoo) Finland, [email protected]

fax: +358-9-451 3856

2) Helsinki University Development Services, Helsinki, Finland

The aim and background

The aim of the study was to examine the performance of a new full scale biological

leachate treatment plant in demanding Nordic winter conditions and to study factors

affecting the process, especially nitrogen removal, and its feasibility including

economical aspects.

The treatment unit consisted of an activated sludge process with predenitrification and

nitrification stages. The process configuration and design values were based on the pilot

scale results found earlier (Pelkonen et al.1999). The construction of full scale plant

started in summer 1999 and was taken in operation at the end of november 1999. The

water taken into the process consisted mainly of leachate from a 2.5 ha landfill (age 7

years) and from an approx. 1 ha windrow composting area. The water was led to a

balancing tank, from where it was pumped to the treatment process. During the winter

and spring period the water temperature was around 2 - 4 C, the hydraulic retention time

1.5 – 3.8 days and the sludge age over 30 days. Phosphorus was added to the process to

maintain the nutrient balance.

Results and discussion

The loading of the process was increased stepwise during the first two months after the

start of the process to allow the adaptation of the biomass. Results after this period

representing winter and spring conditions with snow melting period (length approx. 3

months) are shown in table 1.

Table 1. Treatment efficiency during the winter and spring period

Influent Effluent

Removal efficiency

Unit Avg std Min Max Avg std min max N avg *CODtot Mg/l 619 101 540 820 189 23.8 154 224 7 69.4BOD7 Mg/l 227 48.3 170 290 11.2 3.5 6 15 5 95.0Ntot Mg/l 84 11.4 66.4 97.6 38.3 9.1 32.2 56 6 54.4NH4-N Mg/l 77 8.7 61.7 90.8 1.2 2.5 0.1 7.4 8 98.5NO2+NO3-N Mg/l 25.0 10.8 16 50.7 8Temperature C 6.6 2.3 4.7 11.4 8

*unit %

Avg = average, std = standard deviation, min = minimum, max = maximum, N = number

of observations

The results show a nearly complete nitrification, the ammonia removal was in average

over 98 %. A reasonable denitrification was found, in average the total nitrogen removal

was approx. 55 %. The lowest monthly process temperature was 4.5 – 5 C, which can be

characterised extremely low. It is obviously first time, when a full and stable nitrification

has been reported in a leachate treatment process in this temperature range in full scale.

Removal of BOD7 was in average 95 % and of COD approx. 70 % indicating efficient

degradation of biodegradable organic matter. The residual COD was in average 190

mg/l. The COD- and BOD7- concentrations in the influent were lower than during the

previous pilot tests mainly due to obvious increase in gas production in the landfill and

decrease of organics in the water phase.

The specific nitrification rate was 0.009 – 0.02 g NH4-N (g VSS) –1. This didn’t differ

considerably from the pilot tests, in which the temperature range was approx. 7 –11 C.

These results support to extend the feasible temperature range for nitrogen removal down

to 4.5-5 C. An important factor to take into consideration is the possible inhibition of

nitrification due to heavy metals or other toxic compounds, which can have a synergetic

effect with the decreasing temperature. These results (and other test results not shown

here) indicate that at least in this case this phenomenon didn’t have a remarkable role.

Of importance is, in spite of carbon and nitrogen removal, the solids separation

efficiency, because excess solids deteriorate the effluent quality. Results in table 1 and

other test results (not shown here) confirm a reasonable bioflocculation and that the solid

particles can also be removed without serious problems in an activated sludge process in

these temperature conditions.

The operation and investment costs were estimated in the pilot study and the real data

from this full scale plant confirms that the costs of local biological treatment per m3 and

per kg nitrogen removed are competitive. An important factor was that no extra heating

was used and the energy consumption was low. The good treatment results at low

temperatures aid also the process economy.

Conclusions

A biological process was applied succesfully to treat cold leachate in winter conditions in

full scale. A complete ammonia nitrogen oxidation was maintained, obviously first time

in full scale at process temperature 4.5 – 5 C in combination with a reasonable

denitrification efficiency.

The process was not considerably affected by inhibition due to heavy metals and toxic

compounds in these extreme conditions. Also the solids removal was reasonable.

The treatment results together with economical evaluation show that the application of

biological processes in leachate treatment at low temperatures is worth considering and

the feasible temperature range can be extended down to 4.5 – 5 C.

Reference:

Pelkonen M, Kotro M, Rintala J 1999: Biological nitrogen removal from landfill

leachate: a pilot scale study. Waste Management & Research 17, 493-7.

32

ENHANCEMENT OF WASTE DEGRADATION WITH LEACHATE

RECIRCULATION AT AN OLD LANDFILL

Pelkonen Markku 1) , Nykänen Vesa 1)

1) Helsinki University of Technology, Laboratory of Environmental Engineering

PO BOX 6100, FIN-02015 HUT (Espoo) Finland, [email protected]

fax: +358-9-451 3856

Introduction and the objective

Waste degradation in a landfill in Nordic climate has its own features. A considerable

proportion of the annual precipitation is formed by snow and during the snow melting

period this water storage is released rapidly. The waste temperature in the landfill is

normally rather low ( 5 – 25 C). The acidogenic phase can be expected to have a longer

duration than in warmer circumstances and the transport of carbon trough the water

phase is of importance. In this context the waste temperature and humidity can vary

considerably trough the year and at low temperatures the degradation rate is decreased.

This will imply that emissions are lasting longer and a management problem will occur

trough the long aftercare period.

The objective of this work was to study the behaviour of a completed landfill, when

leachate recycling is applied. The 17 ha landfill (Seutula, Vantaa) was in operation

mainly 1974 – 1987 and was later covered with a surface layer. The leachate is collected

to an equalisation basin, from where it is pumped to a municipal sewage treatment plant.

A gas collection and utilisation system was completed in the mid- 1990’s and the gas

production has also an economical impact.

Materials and methods

During the experiment the leachate from the equalisation basin was directed to two areas

and a third (reference) area without leachate feed was also included. The pumping rate of

water was measured continuously and the feed of water was changed between the two

areas with approximately two weeks intervals. In each area the water was led trough three

wells to maintain a more equal distribution. The recirculation period during the warmer

half year was approximately three months and the feed rate was 0.5 – 1 m per year.

Several parameters were monitored in the water phase in different locations of the three

areas, ie. water level, temperature, pH, conductivity, COD, BOD7, NH4-N, PO4-P,

chlorides, heavy metals, the amount of active biomass and AOX. The landfill was

monitored also in each gas well (total of 19), ie. gas flow and methane concentration as

well as pressure in the wells. Some periodic measurements were made about the emitting

gas trough the landfill surface. An overall picture was attempted to find out before,

during and after the recirculation period.

Main results and conclusions

The true classification of observation points was made based on the behaviour of water

level, which started to rise if the point was affected by the water feed. Some channeling

of water flow could be found.

As a summary an increase in BOD7, COD and NH4-N-concentrations in the water phase

in monitoring wells was found if affected by the recirculation. The BOD/COD ratio

correlated well with the temperature (with a negative sign). These findings indicate an

enhanced degradation of waste due to recirculation, but the gas production was limited by

the temperature.

From the basis of gas measurements a clear difference in gas production could be found.

The gas production before and at the end of the recycling period in the three areas

increased by 55, 12 and 70 %, where the lowest value is for the reference area. Hence

approximately a 50 % increase in gas production can be estimated.

Also some other water quality parameters were affected by the recirculation, but the

variability in general could be rather large (discussed in detail in the full paper). In these

conditions no differences could be found in the AOX-concentratrions when compared the

recirculated areas with the non-recirculated ones.

To enhance the degradation more permanently a through the whole year recirculation

system is suggested due to the long winter period taking into consideration the heat

balance.

33

ANALYSIS OF LEACHATE TREATMENT TECHNOLOGIES

Dr. Hani Abu Qdais. Civil Engineering Department, Jordan University of Science & TechnologyP.O.Box 3030, Irbid Jordan, Email [email protected]

Despite the intensive efforts that are directed to the recycling and recovery of solid

wastes, landfills remain and will remain an integral part of most solid waste management

plans. One of the byproducts of the landfilling process is the generation of leachate. Once

the precipitation occurs, the water percolates through the waste matrix in the landfill and

several chemical and biological reactions are taking place. As a result, organic and

inorganic compounds leach out from the waste leading to the formation of high strength

wastewater known as leachate. Unless managed and treated properly, leachate will lead to

adverse environmental impacts such as odor and groundwater contamination.

Various methods and technologies were proposed and applied to treat the landfill

leachate. These methods are ranging from simple methods, such as recirculation of

leachate through the landfill to a sophisticated process, such as combination of physical,

chemical and biological processes. The applied treatment methods have various degrees

of success. Some were very efficient in leachate treatment, while others were not. This

variability in the treatment efficiency may be attributed to the fact that, the process

designers are ignoring the temporal and spatial variation of the leachate characteristics.

This paper will review the methods of leachate treatment with special reference to the

recent trends in treatment processes. The factors that affect the composition of leachate

from a certain landfill such as, landfill age, waste composition and climatic conditions are

discussed. The impacts of these factors on the selected treatment technologies are

identified. The information and analysis in this study will serve as guidelines for better

decision making in selecting proper leachate treatment processes, so as to mitigate the

adverse environmental impacts associated with the leachate generation.

34Abstract

Aerobic vs Anaerobic Bioreactor Landfill Case Study – The New River Regional Landfill

Dr. Debra R. Reinhart*, University of Central FloridaDr. Timothy Townsend, University of Florida

The New River Regional Landfill (NRRL) in north Florida is hosting a Florida Bioreactor demonstration project. The primary goal of the landfill bioreactor demonstration project is to design, construct, operate, and monitor a full-scale landfill bioreactor in Florida in a manner that permits a complete and fair evaluation of this technology as a method of solid waste management in Florida, with appropriate consideration of science, engineering, environmental and economic issues.

The demonstration will include recirculation of leachate, injection of air into portions of the landfill, and the ability to monitor gaseous emissions from the bioreactor. The landfill bioreactor will be instrumented for the purpose of collecting in-situ measurements of such parameters as leachate head on the liner, and moisture content and temperature of the waste.

The landfill bioreactor at the NRRL is designed to allow operation and testing of both

aerobic and anaerobic waste treatment regimes. The landfill bioreactor will be divided

into two overall zones, a dedicated aerobic zone and a dedicated anaerobic zone. An area

between the aerobic and anaerobic zones will serve as a transition zone. A second

transition zone will be located between the anaerobic zone and the open working face of

the landfill.

Solid waste sample collection will commence during the construction of the injection

wells. When the construction of the bioreactor is completed, the first period of operation

will consist of baseline data collection involving monitoring gas generation and

composition, landfill temperature, and leachate quality. The startup of the anaerobic zone

will consist of the controlled recirculation of leachate and/or other fluids (groundwater or

wastewater treatment plant effluent and biosolids). Aerobic treatment will begin with

controlled air injection into a small area of the aerobic zone. During startup phase, the

aerobic zone will be very carefully monitored for temperature, off gas composition, and

moisture content. The purpose of the start-up phase is to assess responses in landfill

conditions as a function of limited air or leachate injection. Following the startup period,

the routine operation phase will begin, consisting of the normal planned operation of the

bioreactor. Activities during this phase will depend on the results gathered in the startup

phase, but in general will consist of a targeted strategy of injecting leachate and/or air

into appropriate areas of the landfill.

Construction of bioreactor components is expected to begin in summer 2000 with

operation commencing in fall 2000. This presentation will contrast design/control

aspects of operating the landfill in an aerobic vs. anaerobic regime. In particular, the

following will be addressed:

projected construction and operating costs required to support each regime moisture balance issues flammability issues related to gas composition expected leachate and gas quality process control approaches

*Debra R. ReinhartAssociate Dean for ResearchCollege of EngineeringUniversity of Central FloridaP.O. Box 162993Orlando, Florida 32816-2993(407) 823-2156Fax (407) 823-5483e-mail [email protected]

35

Abstract

Upgrading landfill disposal in Kosovo

Since the return of the Albanian Kosovar population to Kosovo in mid-1999 restoring a credible waste management service has been seen as one of the municipal priorities to protect public health. Most effort was initially focussed upon re-establishing waste collection services, more recently attention has turned towards the use of land disposal. Open dumping is the routine disposal method at present and the challenge set for the international and local organisations has been how to upgrade such sites with only modest amount of new equipment, materials and finance.

The paper will focus on describing the present landfill situation across Kosovo and then present the emerging programme to upgrade disposal facilities that is being attempted over the next two years:

1. The most basic intervention necessary is to improve, with local resources only, the existing city open dumps so as to reduce their immediate or most acute environmental impacts and to give them a further two years of operating life. These modifications are intended to also make it easier to leave the sites in a reasonably secure and safe manner at the end of the two-year period.

2. In parallel to the conversion of the open dumps to controlled dumps, some new, intermediate landfills will be set up in and around smaller towns and districts to entice waste away from river dumping and fly-tipping. These temporary landfills will be designed to have a two-year life and will resemble the intermediate landfill design concept described in recent World Bank and WHO publication on this topic.

3. A separate site selection and design team will identify and develop new, more permanent landfills to become regional land disposal sites. It is intended that these will be of a higher standard and have a minimum capacity for ten years of waste input. The precise design standard achievable, given the likely local and international resources available, is still open to debate but it is envisaged that it will take around two years to get these sites agreed and ready to receive wastes. The final landfill design and the locally sustainable finance that will be available are still to be determined and it is intended that the presentation will conclude with a debate on this issue to solicit original ideas for consideration back in the field.

In addition to this Kosovo-wide strategy, donors have instigated other local landfill developments. At one place a mall landfill has been constructed in a reasonably impermeable geology with a reed bed artificial wetland to treat leachate. The paper will include an account of the first few months operational experience of the reed bed system.

Philip RushbrookRegional Advisor, Waste ManagementWHOVia Francesco Crispi 10I-00187 RomeItalyTel: +39 06 4877540Fax: +39 06 [email protected]

36Influence of different artificial weathering methods on the longterm leaching behaviour

of thermal residues from municipal solid waste incineration

SABBAS T., HUBER H., LECHNER P.

Universität für Bodenkultur Wien (University of Agricultural Sciences, Vienna)IWGA, Department of Waste Management

Nußdorfer Lände 29-31, A-1190 ViennaTel.: ++43-1/318 99 00 –34Fax: ++43-1/318 99 00 –50

Modern society puts a lot of pollutants into circulation. Most of them are then enriched in artificial created sinks like multibarrier landfills. Due to the fact, that the technical barrier systems will not last forever, it depends on the middle and long term behaviour of the wastes itself („inner chemical and physical barrier“), if the landfills will become a source of contamination again.

Besides the chemical composition, the physical properties, and the environmental forces the mineralogical composition affects the leaching behaviour of inorganic wastes particularly. Especially the mineralogical composition of thermal treated wastes und stabilization products shows metastabile phase conditions. During ageing processes thermodynamic equilibrium with the environment is strived for, whereby a sequence of secondary mineral neoformations and transformations (oxide – hydroxide – carbonate – silicate - ...) is passed through. Simultaneousely with the mineral alterations the solubility and the physical behaviour of the seepage water is therefore affected.

The aim of the research project was to characterise the sequence of secundary minerals of seven thermal treated wastes and to compare the temporal development of the metal mobility. For this purpose the thermal residues were artificially aged under five different environmental conditions.

aeration with watersaturated air aeration with watersaturated oxygen aeration with watersaturated CO2

storage in humid anaerobic atmosphere storage in humid anaerobic atmosphere and 80°C

Subsequently, by means of different leaching tests, the influence of the varying environmental conditions and their age (declining pH-value) on the metal mobility were investigated. Synchronousely mineralogical tests were performed.

The results show, that the weathering processes are able to mobilize or demobilize metals and salts up to three magnitudes. The rating of the varying artificial weathering methods in combination with different leaching methods will form the conclusion of the presentation.

37Development of a prediction model for the assessment

of the middle and long term emission behaviourof inorganic wastes

SABBAS T., RAUTNER T., LECHNER P.

Universität für Bodenkultur Wien (University of Agricultural Sciences, Vienna)IWGA, Department of Waste Management

Nußdorfer Lände 29-31, A-1190 ViennaTel.: ++43-1/318 99 00 –34Fax: ++43-1/318 99 00 –50

e-mail: [email protected]

Existing leaching and extraction tests in Austria and the European Union describe the emission behaviour of wastes in an unaltered and unweathered state. But they do not describe, how the wastes will behave in middle (after 50 years, when the technical barrier may be leaking) and in long term after natural weathering, and how great the impact will be on drinking water of future generations, due to the changing emission rates. Therefore existing and modified test methods have to be evaluated, to be able to see to what extent they reflect natural leaching behaviour of longterm weathered wastes.

In our project, leachates originating from landfills with inorganic, polluted and weathered wastes are compared to the results of a combination of artificial weathering methods, leaching tests and rated influencing factors (infiltration,...). The investigated materials include bottom ashes and ashes of MSWI, hazardous waste slags, steelslags, solidification products and natural gravel containing ore. The leachates of the weathered materials are collected and specified. Corresponding fresh materials are artificially aged, leached and the results in combination with infiltration are then compared to the leachates of the weathered materials. This method will then allow the assessment of the stability, the transfer factors (waste environment) and thus the impact on drinking water of future generations.

The preliminary data show a conformity in the heavy metal-contents of the leachate of artificial weathered materials compared to the leachate of landfills containing the natural weathered material. Regarding the salts, there are differences in the contents due to the different liquid/solid-ratios in the landfill and in the test. Furthermore the pH and the conductivity of the landfill leachates show no dependence on the changes of the infiltration. In combination with the leachate quantity this indicates that in our landfills preferable leachate paths do not exist.

The results of these investigations, especially the development of the testing-methods, and a comparison with the natural leachates and the prediction model will be presented.



METHANE OXIDATION AND DEGRADATION OF HALOGENATED ORGANIC COMPOUNDS IN LANDFILL GAS AFFECTED SOIL

Charlotte Scheutz4 & Peter KjeldsenDepartment of Environmental Science and Engineering


IntroductionWaste deposited in a landfill will undergo anaerobic decomposition resulting in generation of landfill gas, which is transported through soil top covers causing emission of gas into the atmosphere. Besides methane (55-60 vol.%) and carbon dioxide (40-45 vol.%) landfill gas also contains numerous trace compounds (up to 5 vol.%) (Brosseuau & Heitz, 1994). The trace compounds originate from hazardous materials deposited in the landfill or from biological/chemical degradation of materials deposited in the landfill. Emission of methane from landfills accounts for between 7 and 20% of the global anthropogenic sources of methane emissions thus contributing to the global climate change. Emission of trace compounds like benzene and vinyl chloride to the ambient air can be a threat to workers and local habitants, while other trace compounds like freons contribute to the depletion of the ozone layer (Christensen & Kjeldsen, 1995).Microbial oxidation of methane in aerobic soils plays a significant role in reducing the emission of methane to the atmosphere. In landfill top covers methane and oxygen counter-gradients may appear due to emission of methane from the waste and diffusion of oxygen from ambient air. Oxidation of methane by methanotrophic bacteria in landfill top cover soil has been shown to reduce the amount of methane emitted to the atmosphere. Under methane-oxidating conditions the methanotrophic bacteria is known to co-metabolize a variety of aliphatic compounds including some halogenated hydrocarbons (Oldenhuis et al. 1989).The objective of this study was to investigate the potential of natural oxidation of methane and halogenated organic compounds in soil exposed to landfill gas. In addition, the impact of individual factors (like soil moisture, soil temperature, co-inhibition and concentrations of oxygen and methane) on methane oxidation and co-oxidation of selected trace compounds was studied. The investigations have been carried out through laboratory experiments. The chosen trace components included six chlorinated ethylenes (perchloroethylene, trichloroethylene, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and vinyl chloride), and two freon compounds (chlorodifluoromethane and dichlorofluoromethane).

MethodsThe degradation of trace components was examined in simple batch experiments using soil samples collected from soil covers at Skellingsted landfill, Western Sealand, Denmark. A fixed amount of soil was added to a 117mL batch container equipped with buthyl rubber stoppers, which enabled gas sampling for analysis. Column experiments simulating a landfill top cover soil matrix through in which gas was transported were carried out to examine the degradation process


in a dynamic system. The oxidation process was examined in a methane and oxygen counter-gradient system. The columns were packed with landfill cover soil and water, and continuously fed in opposite ends with methane gas containing trace components and air. Sampling ports located along the column length allowed taking gas samples, which were subsequently analyzed by gas chromatography.

Results & DiscussionHigh methane oxidation potentials were found in batch experiments conducted with soil collected from 5 to 35 cm depth. At 40 cm depth the methane oxidation activity decreased dramatically, but experiments conducted with soil from 90 cm depth showed that there still was low activity at that depth. Degradation of compounds: All the chlorinated ethylenes were shown to be degraded in presence of oxygen and methane, and the degradation occurred in parallel with the oxidation of methane. However, total transformation of perchloroethylene was not observed. In general, the degradation rates and extent of degradation of the chlorinated ethylenes was inversely related to the chlorine/carbon ratios. HCFC-21 and HCFC-22 were also shown to be degradable. Impact of individual factors: The highest degradation rates were obtained in experiments run without methane but containing resting bacteria pre-incubated with methane. Increasing methane concentrations resulted in decreasing degradation rates - a result of the competition between methane and the halogenated compounds for the enzyme methane monooxygenase inducing the oxidation. In batch experiments without oxygen no degradation occurred within the run of the test. The oxidation of methane and halogenated organic compounds was very dependent on temperature, showing optimum rates between 20 and 27C. However, oxidation occurred at temperatures as low as 2C. Batches with a water content of approximately 25 %w/w produced maximum oxidation rates. In experiments with air-dried soil it seemed to be difficult the recover the oxidation activity of the bacteria. The column experiments will be finished during the summer and the results have therefore not yet been analyzed.

Simple calculations based on the obtained oxidation rates from the batch experiments and assuming realistic fluxes of landfill gas and an

oxidation zone of 40 cm showed that the emission of trace components from landfills may be significantly reduced due to degradation process in the soil top

cover.

ReferencesBrosseau, J. & Heitz, M. (1994): Trace gas compound emissions from municipal landfill sanitary

sites. Atmospheric Environment, 28, pp 285-293.Christensen, T. H. & Kjeldsen, P. (1995): Landfill emissions and environmental impact: An

introduction. In: Christensen, T. H., Cossu, R., Stegmann, R. (eds), Sardinia ´95, Fifth International Landfill Symposium, S. Margherita di Pula, Italy 2-6 October, Proceedings, Vol. III. Pp. 3-12. CIAS-Environmental Sanitary Engineering Center. Cagliari, Italy.

Oldenhuis, R., Vink, R. L. J. M., Janssen, D. B. & Witholt, B. (1989): Degradation of chlorinated aliphatic hydrocarbons by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied and Environmental Microbiology, Nov. 1989, pp. 2819-2826.

39

CHARACTERISTICS AND MECHANISM OF SEMI-AEROBIC LANDFILL

ON STABILIZATION OF SOLID WASTE

Takayuki Shimaoka, Yasushi Matsufuji,

and Masataka Hanashima

Department of Civil Engineering, Faculty of Engineering, Fukuoka University,

8-19-1 Nanakuma, Johnan-ku, Fukuoka, 814-0180, Japan

The details of a semi-aerobic landfill are described and compared with an aerobic

landfill, particularly related to the characteristics of the solid waste stabilization and the

stabilization mechanism.

Semi-aerobic landfill is an attempt to lay the leachate collection pipe,

comprising the perforated main and branch pipes and gravel, at the bottom of the landfill

to discharge leachate out of the landfill as quickly as possible. This prevents leachate

from penetrating into the ground water by removing leachate remaining from the bottom of the landfill.

Also, oxygen in air is led into the landfill through the leachate collection pipe by heat

convection resulting from differences between the inner temperature and outside air

temperature. The leachate collection pipe of a semi-aerobic landfill has the following

effects: acceleration of leachate discharge ensures expanding aerobic atmosphere and

improves activities of aerobic bacteria, decomposition of solid waste, and leachate quality.

Comparative study of the decomposition characteristics of the pollutant

components in the semi-aerobic and anaerobic landfills has been conducted by using two

types of large lysimeters (diameter of 1.2m and height of 9.25m). Clarified differences between

landfills are as follows: decomposition of the BOD and T-N components in the seepage

water in the bottom layer close to the leachate collection pipe of the semi-aerobic lysimeter

was clearly evident, and elution of the pollutant components not in the vicinity of the leachate

collection pipe was more remarkable than the anaerobic landfill, suggesting that

decomposition of the waste itself is accelerated.

40Efficiency of Landfill Leachate Treatment by Freeze CrystallizationandNatural Process of Snow Metamorphism

Janusz A. Szpaczynski, Ph.D., ([email protected]) [email protected]

in collaboration with

Jeffrey A. White, P. Eng., ([email protected])

Delta Engineering, 2301 St. Laurent Blvd., Ottawa, Ontario, K1G 4J7, Canada(Tel.613-521-0348, Fax 613-521-8533)

ABSTRACT

In the past, various attempts have been made to apply, in full-scale, the beneficial effect of the freeze

crystallization phenomenon. However, in most of the studies, the process has not been widely accepted

because of its high-energy consumption of the refrigeration system, or, in the case of freezing in natural

conditions, because of the problem with distribution and freezing of large volumes of wastewater. These

problems can be avoided by freezing the wastewater in the form of man-made snow.

The process responsible for segregation of chemical elements and nutrients in the snow pack, as well as its concentration, is snow metamorphism. Snow, as a thermodynamically unstable material, has the ability to change its physical characteristic even at very low temperatures. Fresh man-made snow is a composition of frozen droplets and in macro scale, is dissimilar to natural snowflakes. However, the process of metamorphism is governed by the same mechanisms. Based on this process, as well as the phenomenon of ions elution and its concentration in melt water, authors of the following paper hypothesized that the snow metamorphism process could be applied to treat/concentrate landfill leachate.

After wastewater atomization, the ice crystals first form from the pure water at the surface of each droplet, and trap dissolved compounds such as salts and gases, as well as solid particles in the ice globule. Growing further ice crystals, incorporate water molecules and concentrate compounds in the remaining liquid inside the droplet. As the ice crystal grows, the free space for liquid decreases and the concentration at the growing ice front is higher than in the bulk water. When the solubility of the gaseous compounds reaches the maximum and oversaturation takes place, gas bubbles nucleate and are trapped between the growing ice crystals. An analogous situation occurs with other compounds and some salts may precipitate. The pressure of liquid inside the ice droplet increases with the decreasing volume of remaining liquid. The ice globule may fracture and the concentrate could be released outside. This gives additional benefit for further concentration because the concentrate is removed from the inside of the droplets on their surface. At that moment, the separation and concentration is in macro scale of each droplet and the contaminants are equally distributed in the snow pack profile. However, soon after the man-made snow is deposited on the ground, the temperature gradient is established in the snow pack profile. The mechanism of snow metamorphism, based on vapor pressure gradient, takes place and is enhanced by fluctuations in ambient temperatures. Some ice grains or portions sublimate and the water vapor condenses as pure ice on the surface of the ice grains located in the area with lower vapor pressure. As a result, solid particles and ionic compounds, as well as gas bubbles (volatile compounds of wastewater) are easily excluded and released from the ice. Most of the contaminants are deposited on the surface of the ice grains in the pores of the snow pack. When the melting begins, the rejected and accumulated soluble impurities on the ice crystals are similarly washed down as “cake” in a filtration process. Volatile compounds are stripped away during

atomization and/or separated in frozen droplets as gas bubbles, and slowly released during snow metamorphism and melting.

The efficiency of concentration for non-volatile compounds is described as follows:

Where: a, b, d = coefficients of concentration (based on experimental data).

Concentration of compound “i” in the effluent melt water and in the concentrate (Figure 1) can be calculated from the following equations:

Where:CE(i) = Average concentration of compound (i) in effluent [mg/l];C0(i) = Concentration of compound (i) in raw wastewater [mg/l].

Figure 1 Concentration Curve

Selected results from concentration of landfill leachate in lab scale experiments are presented. An elution

of anions and cations, as well as other parameters during the melting process, were monitored. A high

concentration of contaminants was reported in the initial runoff of melt water. Most toxic elements and

organics were concentrated in the first melt water runoff. The efficiency of the process was different for

different elements. Sulphate was generally not detectable in the melt effluent. Very high efficiency of the

treatment was also noted for chloride and such compounds as Boron, Potassium and Sodium. More than

95% of these elements were removed from the leachate. An increase in BOD, COD, DOC and TOC, in the

first melt was very high and reached values of 92%, 94%, 95% and 97%, respectively. Satisfactory

concentration efficiency of Barium was also reported (94%). Other elements such as Aluminum,

Chromium, Nickel, Zinc and Iron were concentrated to 93%, 90%, 93%, 89% and 92%, respectively.

Mercury, in raw leachate was 0.0007mg/L and was concentrated in the first 20% of melt to the value of

0.003 mg/L .In further samples of effluent, Mercury was below Method Detection Limit. The concentration

efficiency of Copper was at the range of 77%. Lower concentration of 21% was reported for Fluoride.

Fluoride is easily incorporated into the ice structure and thus its concentration was restricted.

The freeze crystallization process improves clarity of effluent. The colloidal particles undergo natural agglomeration and are easily separated from the melt water stream. The atomizing freeze crystallization process can be an excellent pretreatment unit system in winter operation or may work as a separate independent unit.

41LEACHING BEHAVIOUR OF VAM BIOREACTOR REST PRODUCT AT

DIFFERENT STAGES OF DEGRADATION IN LAB AND PILOT SCALE TIO

ASSESS POTENTIAL UTILIZATION OPTIONS.

H.A. van der Sloot, J.A. Woelders

ECN Petten The NetherlandsESSENT Wijster The Netherlands

Abstract

At VAM a bioreactor study was initiated in 1996 with the mechanically separated organic residue (MSOR) of a waste separation plant at the VAM treatment facility. As in many other studies, the aim of the work was largely focused on the degradation aspect of MSOR. This work focuses on the aspect of the ultimate quality of the end product from the bioreactor for possible reuse. The existing information on the ultimate quality of the end product is limited as in many cases the end product is only considered as a residue for final disposal, therefore not requiring detailed characterization. When the emphasis shifts to possible reuse or changing the disposal regime, more information on the long-term quality of the end product is needed. The characterization of the MSOR described in this work consists of an evaluation of its leaching behaviour to assess long-term environmental impact. Since the material has specific characteristics not common to other materials for which evaluation criteria exist, new criteria for evaluation may need to be developed. These relate in particular to the residual generation of dissolved organic carbon, which acts as a carrier for trace contaminants – both inorganic and organic, morphological aspects and environmental impact. This work aims at characterizing the leaching behaviour at different stages of the degradation process in the bioreactor to be able to predict material behaviour in the long term. The residual release of contaminants in dissolved organic carbon (DOC) associated form is a key issue in this respect. The use of DOC measurement at neutral pH as a means of establishing the status of degradation will be discussed in relation to measurements carried out after 2.5 years of degradation in the full scale pilot. This also allows a comparison between the leaching behaviour of material degraded under optimal conditions at laboratory scale (3 m high columns) and material degraded in the pilot scale.

42Organic Matter Stability after mechanical-biological Pretreatment of MSW

Alexander ZachUniversität für Bodenkultur, Wien, Abteilung Abfallwirtschaft

(University of Agricultural Sciences, Vienna, Dept. of Waste Management); Nußdorfer Lände 29-31, A-1190 Wien, AUSTRIATel.: ++43/1/3189900-43, Fax: ++43/1/3189900-50

E-Mail: [email protected]

AbstractStabilized, mechanically-biologically pretreated wastes (MBP-wastes) still contain up to 30 % of organic substances. Biological tests, however, indicate, that these materials are largely stable and non-reactive. When landfilled can the objective of waste stability be uphold despite the high content of organic? Can stability last forever or will organic matter change during the time of deposition? Do we have to expect release if conditions change?This paper focuses organic matter of MBP wastes. It is investigated how – apparently stable – solid organic material can be characterized and how it behaves during a 1.5 year period of deposition. Different parameters were used for characterization, looking at easy degradable, long-term degradable and non-degradable organic matter. Special focus was put on the investigation and behavior of humic substances which represent the major part of stable organic matter.

During the deposition of MPB waste a change of organic matter could be observed, depending upon the degree of stabilization. Ignition loss and consequently, the amount of organic substances, above all cellulose, decrease. 60 - 80 % of the – anyway small – gas generation can be ascribed to the reduction of cellulose. A part of the gas generation can be explained by degradation of easy degradable organic substances, i.e. proteins, carbohydrates and to some extent fats. However, chemical analysis of stabilized MBP-waste still determine about 40 % of the total organic substance as easy degradable, although no further biological reactivity could be observed. For explanation parallels to soil science could be helpful. According to soil analysis 1/3 of soil organic matter consists of not yet degraded carbohydrates, lignin, enzymes, proteins and lipids. Their stability can be explained by protection from degradation through covalently binding to other, non degradable substances, sorption and integration or inclusion into organic or inorganic particles. Soil science assumes centuries, when speaking about availability from enclosed organic substances. A considerable part of the organic substance are humic substances. Depending on the residual reactivity of MBP-waste the content of humic substances remains either constant or even increases during the time of deposition. Increase could be a result of the presence of potentially reactive intermediary products from degradation. Humic substance release in the leachate is negligible, which underlines their stability. It was found that organic substance of MBP-waste contains up to 13 % of humic acids. Based on literature data humic acids represent about one half of the total humic substance (= fulvic acids + humic acids + humine). Consequently, the total amount of humic substances is roughly 1/4 of total organic substance and thus still far away from values that are found in soil (2/3 of organic substance). This may indicate that there is still a potential for degradation. If the amounts of humic substances and plastics are summed up a good estimation for the biological stable fraction could be gained. Investigations show that about 30 % of the total organic carbon are bound in humic substances and are to a large extent stable. Equally, a high amount of nitrogen could be found in humic substances of MBP-waste. Various further analysis point out that nitrogen is built into humic substances. Therefore it can be concluded that humification has a positive effect on nitrogen release, leading to retention or a " slow release effect ".Finally, more efforts should be undertaken to characterize composition and behavior of apparently stable organic matter of MBP- and already landfilled waste to understand processes that might happen in the future. For long term - if MBP-waste might approximate soil like characteristics - organic substance must be degraded anyway and thus a strong reduction of by now stable substances must take place. But this might happen over year, decades or even centuries – in periods compatible with natural environmental cycles.

43ABSTRACT

Submitted to theIntercontinental Landfill Research Symposium

Lulea University of TechnologyLulea, Sweden

December 11-13, 2000

IN-SITU MOISTURE CONTENT MEASUREMENT AND CONTROLIN BIOREACTOR LANDFILLS

Dr. Chris Zeiss, P.Eng. and Dr. R. LiDept. of Civil and Environmental Engineering

University of AlbertaEdmonton, Alberta T6G 2M8

CanadaTel. (780) 492 5122Fax (780) 492 8289

Email: [email protected]

Moisture content is the most important factor for enhanced biodegradation of solid waste materials. Measuring the moisture content and achieving an optimally high and evenly distributed moisture content within packed layers of heterogeneous solid waste materials is, however, a serious challenge for solid waste engineers, bioreactor landfill operators and for waste management researchers. The goal of the research presented in this paper was to test and develop a reliable and accurate system to measure the in-situ moisture content of solid waste materials based on the principles of time-domain reflectrometry (TDR). TDR sends an electro-magnetic wave along waveguides through a porous medium. The reflection time of the wave principally depends on and varies with the moisture content of the porous material. Although the TDR principle is simple and has been used extensively in soils, its application to solid wastes creates special challenges: 1. Solid waste materials are heterogeneous, and, in particular, vary in their in-situ porosity, organic content, ferrous metal content; 2. Leachate electrical conductivity (eC) significantly affects the sensitivity of the TDR signal and varies by location in the landfill and over time as the leachate strength changes. As a consequence, the calibration of the values measured by the TDR probes with the volumetric moisture content changes depending on the type of material – and in particular its porosity – and the electrical conductivity of the liquid (leachate).

An experimental program was developed to test the effects of a) material types (paper, yardwaste, plastic, glass, metal, and sand, as a comparison soil) and material combinations (yardwaste and paper, plastic and glass), b) porosities of the in-situ material, and c) electrical conductivity of two liquids (tap water with a low eC of 0.03 S/m, and leachate with a high eC of 2.4 S/m). Subsequent tests were conducted with coated TDR waveguides and with the common blank steel TDR waveguides in an attempt to reduce the signal attenuation that limits the upper moisture content a TDR probe can reliably measure, particularly in high eC liquids. Two general forms of calibration equation were adopted and tested for fit with all combinations of materials, liquids and the two types of waveguides: a fourth-degree polynomial and a customized third-degree polynomial form.

Where parameters a, b, c, d,and e are to be determined

The results of the experiments and of the subsequent analysis support four important findings:1. Both forms of general calibration equations provide excellent fit (R2 values over 0.98) and good reproducibility for all materials, albeit with slightly different coefficients for each type of material.

2. Differences between materials can be accounted for by the in-situ porosities, because the porosity determines the maximum (i.e., effectively saturated) moisture content. Thus, different waste materials with similar in-situ porosities exhibit similar calibration curves and coefficients in the polynomial equations.3. Different TDR calibration curves must be used for high and low eC liquids. However, the use of coated TDR waveguides significantly reduces the effect of the liquid electrical conductivity.4. Two calibration surfaces are presented to show the relationship between porosity of the waste material, the electrical conductivity of the liquid and the resulting in-situ volumetric moisture content of packed solid waste materials.

The research shows that TDR can be applied to measure in-situ moisture contents in solid waste materials, usually with an accuracy of plus or minus 5 % of actual volumetric moisture content, if the type of material or its in-situ porosity can be estimated or measured. Further, the electrical conductivity of the liquid must be taken into account, which is most easily achieved by measuring the electrical conductivity with the voltage ratio of outgoing and reflected signal at the same time as the reflection time is measured. Thus, the only variable that must be recorded at the placement of the TDR probes inside a bioreactor landfill is the porosity of the material.

The TDR technology can now be integrated into an automatic moisture measurement system for bioreactor (and conventional) landfills. When incorporated with capillary wicking layer system, moisture can be transferred to dry pockets where conventional leachate circulation would not be effective. This moisture enhancement system would improve the biodegradation rate in the landfill. The automated moisture measurement system allows the monitoring of in-situ moisture content as a bioreactor process control system to optimize the biodegradation and gas production. Of course, the TDR system is also valuable as a scientific instrument to track moisture movement and distribution patterns. This system is currently operating on a trial basis in the solid waste management laboratory at the University of Alberta.

Further issues for research include the need to determine the effect of changing porosity with settlement and to measure porosity in-situ. These objectives are under study at the University of Alberta.

Zeiss and Li c:/mydocs/document.doc

carbonation of ca based waste materials from fbc...

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